Parents have hit out at the Child Maintenance Service (CMS), saying it has hiked their arrears and monthly repayments by up to 300% with no explanation.
These parents - both men and women - say CMS mistakes have driven them as far as poverty and homelessness.
Some have even taken their own lives.
The criticism comes as a damning report earlier this month said the number of children getting child maintenance cash is falling, despite the CMS.
The issue surrounds 'non-resident' or 'paying' parents, who after a relationship break-up pay cash monthly to the 'resident parents' that have custody of any children from that union.
Much of the public discussion about child support looks at the problem of so-called 'deadbeat dads' who refuse to pay resident mothers what they owe.
But a second problem has emerged concerning non-resident parents of both genders.
The Mirror has spoken to non-resident parents who say the CMS has hounded them for arrears they do not owe and mistakenly hiked their monthly payments to absurd levels.
Have you been affected by this? Message sam.barker@mirror.co.uk
One such parent, Craig Bulman, 52, says the Child Support Agency (CSA) told him he owed a massive £12,000 in arrears.
The CSA is the former name for the CMS.
The organisation also ignored a pre-existing arrangement he had with the mother of his children, he claims.
The way child maintenance works is that parents can set up a private or 'family-based' arrangement - basically a private agreement on how much the non-resident parent pays. The CMS plays no part in these.
A step up from that is a 'statutory' arrangement, which is an agreement handled by the CMS.
Bulman is a veteran who served in the 2nd Battalion of the Parachute Regiment and Household Cavalry and was also a member of the famous Red Devils, the British Army parachute display team.
Bulman separated from his wife and mother of his daughters in July 1995.
He says he had a voluntary agreement with his ex-wife to pay £200 a month, plus any debts from their marriage, paid directly from his Army salary.
In April 1996, a month or so before being deployed to the conflict in Bosnia, Bulman got a letter out of the blue from the CSA.
The letter asked him to pay £280 a month - well above his means.
By 2008 the CSA was demanding around £12,000 of arrears, which Bulman said he did not owe.
But in 2009 the CSA took out two liability orders for these arrears, giving them extra powers to chase the 'debt'.
Bulman complained about the arrears being wrong, which the CMS ignored.
Instead, they doubled down by taking up to 40% of his salary directly, known as a detachment of earnings order (DEO).
His payments were then £816 a month, and the pressure of making these payments and dealing with the CSA led him to have a breakdown.
Bulman could no longer afford his rent and became homeless.
The armed forces charity SSAFA helped Bulman move back with his elderly mother 300 miles away.
"Where these arrears came from I have no idea," Bulman said. "I had been making substantial voluntary payments, to clear the arrears as quickly as possible, prior to the DEO being enforced.
"I later discovered that I did not owe the arrears and a substantial amount was written off, but by then it was too late. I had already had a breakdown and had been made homeless, and yet another career was damaged by the recklessness of the CSA.
"I could not understand how they believed their actions were in the best interests of my daughters, they just did not care and quite clearly did not care if I could support my daughters or not."
In April 2012 the CSA admitted to Bulman it had mishandled his case and that its liability orders were not called for.
He was awarded a consolatory payment of £5,000.
He says the incident also triggered post-traumatic stress disorder, for which he now claims Personal Independence Payment (PIP)
Another non-resident parent who struggled with the CMS inflating his payments was Gavin Briggs, a veteran of the Royal Air Force (RAF).
Gavin died by suicide in July 2020, but The Mirror has spoken to his father, Ian Briggs.
Ian says Gavin paid child maintenance for three children, one for three years and the other two for two years, until his death in 2020.
After leaving the RAF Gavin became a train mechanic, and earned £52,000 a year.
But Ian said the CMS, when working out how much Gavin should pay, decided that his salary was actually £78,000 a year - £26,000 more.
To make matters worse, the CMS also decided that Gavin owed nearly £16,000 in arrears.
"They added an extra £26,000 to his salary - nobody knows from where," Ian said. "He was very worried about it."
On the day Gavin died he logged onto an online CMS portal and found his child maintenance payments had been increased by almost £1,000 a month, to a total of £2,669.
He had £9 left in his account on that day, Ian said.
Now Ian is campaigning for reform of the CMS.
"I don't want any money or compensation, because that can't bring him back," he said. "I just want the CMS to stop doing what they are doing."
Ian also runs a website that pays tribute to Gavin and his life.
Another non-resident parent affected is John Smith, 55, who says the CMS ignored a pre-existing arrangement to split child support 50/50 with his former wife.
His marriage broke down in late 2009 when he found out his wife was having an affair with his friend and neighbour.
"I walked away with very little from the relationship and had to start again - I'm talking a blow-up mattress on the floor," he said. "I started again with nothing. At points this pushed me to feel like there was no point carrying on."
At points Smith was being ordered to pay inflated payments of £963 a week, which implied a salary of around £1million a year, and was told he owed up to £25,000 in arrears.
The Mirror has also spoken to a non-resident mother, who wants to stay anonymous due to upcoming court dates.
She says the CMS has also hit her with an arrears bill of £5,600, which she says is "made up."
Her marriage broke down after her husband became abusive towards her, sometimes in front of their daughter.
She claims he lied to get custody of her daughter, who she has not seen since 2019, and is now fighting the case in the courts.
Although she is on Universal Credit and earns between £11,000 and £16,000 a year, she has to pay £96 a month in child maintenance to her ex-husband, who earns more than £70,000.
"They just make it up," she said. "At one point it was £2,600, then suddenly it's gone up.
"My view on the CMS is it's not fit for purpose, it is making money out of non-resident parents and making up figures that put these parents under an awful lot of stress."
When parents pay or receive child maintenance through the CMS's Collect and Pay service, they pay a fee each time.
If you use Collect & Pay, a 20% collection fee will be applied to each child maintenance payment and a 4% collection fee will be deducted from the money passed to the receiving parent.
The CMS collected £33.5million in 2020/1, and it was chasing £310million of arrears by March 31 last year.
The anonymous mother added: "Police should listen to women who are victims of abuse, but they ignore us."
Victoria Leonard, 36, is the founder of Family Superheroes, a group of 200 volunteers that supports parents struggling with child maintenance.
Leonard said: "Some are financially abused to the point of poverty by the CMS as they cannot afford these outlandish payments.
"It's not just men. Women can have their kids taken off them and given to the protective father because they have been alienated. There is also a lot of silencing and gagging."
The CMS is part of the Department for Work and Pensions (DWP).
A DWP spokesperson said: "The Child Maintenance Service considers the wellbeing of both parents when establishing the right level of maintenance to support children. Our staff are highly trained to manage very difficult circumstances, and parents can appeal decisions.”
In the past the CSA admitted deliberately inflating arrears by up to 300% to 'scare' parents.
In a 2010 report by MPs, former CSA chief executive Stephen Geraghty said: "most of the very big arrears are these figures which were deliberately made big in order, as I say, to push people into providing data".
However, the CSA claims to have stopped using this technique by 2010.
In December 2017 an NAO report noted that CMS calculation errors meant it could not verify if the £3.7billion in arrears it was chasing was accurate.
