Energy giant EDF sent a woman an £8,000 bill for a home she no longer lives in.
Dawn Gibson told the company she had moved after paying via direct debit at the old property since 2018.
The provider sent her a cheque for £400 after telling her she was in credit but then sent her a bill for £8.117.72 for four years' worth of power.
Dawn, from Spennymoor in County Durham, said: "When I rang EDF to tell them we were moving house they said I was in credit and sent me a cheque for £400.
"A month later I received a bill for the new owners. I rang them and they said not to worry about it.
"Then they sent me a bill for over £8,100."
When she phoned to complain EDF told Dawn her old home had two accounts and the bill was for energy used since March 2018.
The 58-year-old cleaner, added: "It was scary. I had no idea what it was for.
"How they can generate two account numbers and send me a bill for that much when I've already paid is beyond me."
EDF has now apologised to Mrs Gibson and offered her compensation.
A spokesperson said: "We are very sorry for causing Mrs Gibson worry for an incorrect bill she received due to an error on our system.
"We have been in touch with Mrs Gibson to confirm that there is no outstanding amount on her account and she will be sent a new bill to confirm the zero balance.
"We always aim to offer our customers the best possible service and in recognition that on this occasion we fell short, we’ve offered Mrs Gibson a goodwill gesture of £50 which she has accepted."
In April, 46-year-old Paul Davies, of Scunthorpe, was wrongly charged £40,000 a day for electricity.
EDF told him they would be upping his direct debit to £400 a month as a result and despite his protestations that it must be a fault with the smart meter he was told "they're never wrong."
It turned out it was faulty and he ended up having to shut the contraption in a cupboard to stop the problem happening again.
