A system error in smart meters has led to customers being quoted thousands of pounds for a day's usage of gas and electricity.
Confused customers posted the strange readings from their SSE smart meters on social media, with one display showing almost £20,000 for a single day.
Smart meters send information on energy usage directly back to the supplier.
SSE apologised and said no customers would be charged "the extra amounts resulting from errors".
Will smart meters be worth the money?
Smart meters let the customer know how much electricity or gas they are consuming each day - and how much it's costing them - in real time.
But for some customers, the readings have been somewhat higher than usual in the past two days.Image copyright Twitter Image caption Customers took to social media on Friday and Saturday
Usman Hussain, whose meter suggested he had used £9,576.98 of energy on Friday, wrote on Twitter: "Think my SSE Smart Meter for energy and gas may be having slight problems! Either that [or] a neighbour has started nicking my leccy or gas."
For the reading to be accurate, Mr Hussain would need a home bigger than Buckingham Palace - which, with 775 rooms, was billed £1m for a year.
The average annual bill for a large house in the UK is £1,486.
A spokesman for SSE told the BBC: "SSE is aware of the issues affecting a small number of our smart meters.
"The issue will be investigated as a matter of urgency and no customer will be charged the extra amounts resulting from errors with the smart meters.
"We would like to apologise to any customers if this has caused distress."
The government wants every home and business to be offered a smart meter by the end of 2020.