A man said he felt like he was being mugged when he received a £4,000 electricity bill from his energy provider.
Christopher Barnes, 58, said his last OVO bill was £59.82 and he paid it in full on October 11.
The disabled man, who lives in a one-bedroom flat in Jesmond, Newcastle, said he was "shocked" and "appalled" when he received another bill for the amount of £4,190.77 earlier this month.
Mr Barnes said he received no explanation about the reason why his bill was so high and he had to contact OVO, who recently took over SSE, to find out, reports Chronicle Live.
He said the company claimed the bill, which was sent to him on November 10, had come from a balance adjustment from SSE.
He explained: "I felt absolutely shocked and I couldn't believe it was real. There's no way I would be able to afford it. I knew straight away that I would be phoning them up, complaining and fighting it because it is so extreme. It's like being mugged!
"If they are doing this to lots of different people then they are causing huge amounts of distress. There are vulnerable customers who might pay that or commit suicide because of a bill like that."
Mr Barnes added: "It can really affect their mental health. It could terrify them if they already have lots of debt. It could tip them over the edge into suicide.
"I'm absolutely appalled. I can't believe that is legal and, if it is, it certainly shouldn't be. I think they are profiting off the energy crisis."
Mr Barnes said he has always entered his meter readings and paid his bills on time.
He added he was advised by Ovo, via an online chat, that the amount was due to a "balance adjustment" from SSE but he has not been able to get in touch with them over the phone.
He said: "I thought it was a joke, I didn't believe for one minute it could be real. I don't get a reply when I contact them, they are expecting me to pay it!
"I had to contact someone at the company to find out I had been overcharged. If it isn't a mistake, it's definitely their fault. If they overcharged me by such a huge amount it's their calculations that have been wrong, not mine!
"I have been putting my meter readings in online and passing them on to the company. I do that when asked to do so. I have been able to pay the bills so far, but that hasn't been easy."
An OVO spokesperson said: "We are very sorry to Mr Barnes for the shortfalls in service. We can confirm his account is now up to date and we've offered a goodwill gesture for the inconvenience caused."
It comes as other customers who were transferred over from SSE received bills of almost £50,000.
One Ovo customer was asked to pay a £49,000 bill for a two-person home - for just four months of energy use.
She said: "I was assured my account would be put on hold but am now being chased over a bill of £34,015 for the three months to October.
"What started as one of modern life's irritations is now taking up many hours of my week and I’ve hit a brick wall trying to sort it out.
"I’ve cancelled my direct debit, otherwise they would have just taken the money, but I know that shortly they will put this in hands of a debt collector."
