A restaurant owner says she faces financial ruin after receiving a £45,000 electricity bill.
Karen Williams, who disputes the total, said she at first thought she was the victim of a "practical joke".
Ms Williams, owner of the Mulberry Tree, in Boughton Monchelsea, Kent, said the claimed energy usage was "equivalent to a small factory".
Utility Warehouse said she had been undercharged for a decade and the bill represented three years' back charges.
The company had recorded incorrect meter readings since 2008 and realised the mistake in June 2018, Ms Williams said.
However, Ofgem rules in force at the time stipulated businesses could only be billed for mistakes dating back three years.
Ms Williams was sent an invoice totalling £45,108.08 and her monthly bills more than doubled, she said.
Ms Williams said she had previously paid between £150 to £350 each month, which "seemed right for a small, family-run, country restaurant".
Solicitors appointed by Ms Williams' insurers sent an independent electrician who said her meter was recording double the actual electricity usage.
"Apparently it's equivalent to a small factory with 50 employees and heavy machinery," said Ms Williams, who has six full-time employees and several part-time staff.
'Threatened with bailiffs'
She said the bill, which remains unresolved, would "bust the business," adding: "We couldn't sustain a payment like that. It's huge.
"They have threatened me with bailiffs and bankruptcy. It's been hugely stressful."
Solicitor Matthew Knight said that, after complaining to the Energy Ombudsman, Utility Warehouse had been ordered to install a "check meter" at the restaurant.
He said: "If the meter is inaccurate then the £45,000 of back charges will, in fact, be £22,500."
Utility Warehouse said: "We're in contact with Ms Williams directly, and we've complied with requests from the Energy Ombudsman regarding her energy usage."