Complaints to the Energy Ombudsman reached a record level, passing 100,000 last year - with investigators ruling against suppliers in three-quarters of cases.
The figures come amidst growing anger at the pre-payment meter scandal, with harrowing accounts unearthed of vulnerable people's homes being broken into by British Gas subcontractors.
Incorrect billing, poor customer service, and problems switching suppliers were the main issues prompting complaints, the BBC reports.
The number of complaints in 2022 was 50% higher than two years earlier.
There is mounting pressure on the energy sector after sickening details of pre-payment meters being forcibly installed were reported this week.
In the wake of an investigation by The Times, regulator Ofgem ordered suppliers to stop the practice.
The paper's probe revealed how customers - including disabled and mentally ill people - had been forced onto the pay-as-you-go metres, or faced having their gas switched off.
Business Secretary Grant Shapps described it as "outrageous", and the government ordered firms to come clean on how many times it's happened.
Just days earlier, Ofgem's head sparked disbelief among MPs after justifying the practice, claiming some customers chose not to pay their bills despite having the money.
Jonathan Brearley branded the controversial step "reasonable", saying: "There's something I'll say that may not be popular here, but there are a group of customers who can afford to pay their bills but choose not to.
"Everyone is agreed in these circumstances that a mandatory move to a pre-payment meter is a reasonable response to those families who can afford to pay.
BBC Radio 4's Money Box programme reported that a total of 105,340 complaints were received by the ombudsman in 2022, which it said was a rise of more than 50% compared to two years prior.
A spokesperson for Energy UK told the BBC: "With millions of people struggling to pay energy bills as the cost of living soars, more people than ever are contacting their energy supplier for help.
"Customer service teams have seen a fourfold increase in customer contact and are doing their best to respond to the huge numbers of customers getting in touch - often about complex issues.
"Our members work tirelessly to resolve complaints themselves, however where they are unable to come to a resolution with the customer themselves, the Ombudsman plays an important role in making sure complaints can be resolved.
"The question is how you identify a vulnerable group of customers and protect against those who face a much more significant risk when you make that decision."
He admitted he was unable to confirm the percentage of those who had meters forcibly installed because they did not have the money to pay their bills.
By law, companies are allowed to forcibly install meters as a "last resort", but the government has called for suppliers to come clean on how many times they've done it.
Ofgem subsequently ordered all domestic energy companies to suspend the system of forcibly installing prepayment metres, while Business Secretary Grant Shapps described the practice as "outrageous".
It is unclear whether authorities will want to ban the forced switching of customers to prepayment meters.
It is the only way that suppliers can ensure people pay their bills, and companies are only allowed to do so after exhausting all alternative solutions. Former Ofgem boss Dermot Nolan warned that the cost for bills that do not get paid is spread onto all other households across the country, so any ban could hike prices.
