A Mansfield resident said he is prepared to go to court over demands to pay an electricity bill of over £1,200, which he says is incorrect.
Harry Smith of Tuxford Court, Mansfield, switched over to Green Star Energy from Ecotricity after Utility Discount switched his suppliers last year.
However, he said he was 'shocked' to receive an electricity bill of £846.66 for the quarter of September 13 - December 12 2018, when his usual bill would come to around £90.
He later received another demand for a further £433, bringing the total to £1,279.
He said: "It's unreasonable for a small bungalow when it's just me and my wife.
"I noticed that the serial number on the bill didn't match the serial number on my meter.
"I contacted Green Star Energy to tell them to correct the bill, and they promised to call me back but I never heard from anyone".
After Mr Smith took the case to OFGEM, the energy supplier ombudsman, he has since received two emails from Green Star Energy, demanding he pay £1279.00 immediately, which he refuses to do.
Mr Smith added: "I am prepared to go to court over this bill. I have always said that if they send me a correct bill for what I owe I will pay it, but I am being overcharged.
"I have contacted a solicitor who advised me that technically this is not my bill, as it has a different serial number on it to my meter."
OFGEM have contacted Mr smith in the last two weeks to say the case had been resolved and it would be closed, but Mr Smith contested this, and the case has now been passed to a senior adviser.
A spokesman from Green Star Energy said:“Green Star Energy is committed to ensuring the highest level of customer satisfaction. Following our own internal investigation, Mr Smith’s case was then independently reviewed by the Ombudsman.
"The final resolution, a goodwill discount applied to the balance and written apology for any inconvenience, was accepted by Mr Smith.
"Green Star Energy continues to work with the customer to resolve the outstanding balance with a bespoke payment plan.”