John Broomhead wanted to change energy supplier at his Sheffield fish and chip shop to save money.
However, after switching from Npower to British Gas he was landed with a bill for more than six times his normal amount.
John, of Broomhead Fish and Chips in Crookes, said: “I just don’t know what to do. I’m not sleeping because I’m worrying about how to pay it.”
Mr Broomhead’s ordeal began early last year when he swapped provider.
He was sent a final bill, but his meter reading was less than Npower had quoted, so he contacted them to tell them the current reading.
However, to his surprise, Mr Broomhead was then sent a bill for an outstanding amount of almost £4,000.
His quarterly bills always ranged between £400 and £600 - so he could not understand why it had increased so much.
He said: “They said all my bills have been estimates since 2012, but on the back of one from 2013 it says customer reading.
“The five bills I have received since then can’t have been out by nearly £4,000.”
To add to the confusion, Mr Broomhead’s new supplier, British Gas, has also sent a large bill out in error in August.
Npower and British Gas both looked into the matter as soon as they were contacted by Action Desk.
Npower reduced the final bill to just £641.94 after recalculating it.
A spokesman for Npower said there was three meters supplying the property, but only one appeared to be working.
He said: “We are concerned to hear about Mr Broomfield’s query. We’ve recalculated the charges and sent him an amended bill – we’ll also factor in a suitable goodwill gesture, to say sorry.”
And further good news was received by Mr Broomhead when British Gas upgraded his meters to smart meters.
Catrin Millar, of British Gas, said: “We should have acted immediately when Mr Broomhead first raised concerns about his electricity account.
“We’ve fully investigated and confirmed both his meters will upgraded to smart meters.
“We’ve called Mr Broomhead to apologise and explain no further bills will be sent until we receive accurate readings from his new meters.”