A British Gas customer was left gobsmacked after his energy bill stated that he owed over £82,000.
Tim Whiteley, 60, said he was "quite taken aback" by the staggering sum when logging onto his account last week to check his current status.
Thankfully the figure was put down to a meter reading being entered incorrectly, but he was left struggling to resolve the issue for around a week.
Mr Whiteley, who lives in a four-bedroom home with his wife in Lancashire, told the Mirror: "You can imagine it was a bit of a shock.
"I realised it was a system error, it had to be, but despite a number of online chats and telephone calls I never really got a proper explanation as to why it had happened.
"The only explanation I was given was that their system had assumed the smart meter had gone from the previous meter reading all the way around and back to where it was.
"So they were charging me for around 13,000 units of gas in one month."
The error has since been fixed, he added, but expressed concern over inaccurate figures potentially going unnoticed by other customers.
Mr Whiteley said: "My wife was getting quite stressed about it because there was just quite a lack of action really over that period of a week to get it resolved.
"My concern with the £82,000 is if they can just overnight drop a spurious amount into my account, they can do that with anybody.
"With a lesser amount, it would be more difficult to spot. So for example, if they said I was £500 in debit, I might think 'well actually because of the rise in the cost of energy, that's right' and it just is what it is.
"But actually, it was £82,000 so that set the alarm bells ringing. If it was a lesser amount, it might not have.
"How many people out there have had the same problem but haven't noticed because it's a small amount?"
British Gas said it has apologised to Mr Whiteley, whose actual balance is £11 in credit.
A spokesperson for the energy provider said: "This is down to an incorrect meter reading that we entered in error, causing a very high projection that clearly wasn’t right.
"Tim’s actual balance is £11 and we’ve been in touch promptly to explain this and apologise for the confusion."
The comments come as experts warn the price cap on energy bills might rise even more than previously thought.
Gas prices spiked again on Monday and unless they drop in the coming months, average households could be facing an annual energy bill of £4,650 from January and £5,456 from April.
Once again it is the worst warning yet from Auxilione, an energy consultancy. It adds nearly £200 to the consultancy's previous forecast for April.
The price of buying gas for the fourth quarter of this year is now around 100p higher per therm than it was just two week ago, while electricity prices have risen by around £100 per megawatt hour.
One therm cost 563p as markets wrapped up on Monday and a megawatt hour of electricity cost £606.
The new forecast predicts that bills will start falling from July, initially to £4,811 and then to £4,446. But this is still thousands of pounds more than families are paying at the moment.
On Monday, the Labour Party called for the price cap to be frozen at its current level of £1,971 until April to help struggling families through an otherwise disastrous winter.
It is the latest pressure to be put on the Government to add to its £400 help for households with bills that will be paid in six instalments starting in October.
The support was announced in May when experts thought the price cap would only reach £2,800 in October.
