Ten energy suppliers have paid around £7million in compensation and refunds to thousands of customers after an error.
More than 34,000 customers were overcharged on their energy bills over the past six years due to an error, according to the energy watchdog Ofgem.
The affected suppliers include Octopus Energy, Utility Warehouse, Ovo Energy, So Energy, Outfox The Market, Ecotricity, E.On Next, Tru Energy, Rebel Energy and EDF Energy.
The issue occurred between January 2019 and September 2024, with customers being refunded after being incorrectly charged.
Octopus Energy, the UK's largest supplier, paid out £2.64m in refunds and made a £546,278 goodwill payment to more than 20,000 customers.
Utility Warehouse had the second-largest payout, refunding over £2m to 8,272 of its customers who were overcharged.
Ofgem's new energy price cap has come into effect GETTYThe error affected customers with more than one electricity meter point at their properties recording energy usage.
Suppliers can apply multiple standing charges for homes with multiple meters, but this resulted in some customers being "erroneously charged more than is allowed under the price cap".
Charlotte Friel, director of retail pricing and systems at Ofgem, said: "We expect all suppliers to have robust processes in place so they can bill their customers accurately.
"While it's clear that on this occasion errors were made, thankfully, the issues were promptly resolved, and customers are being refunded."
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GETTYShe added: "Today's outcome serves as a reminder to all energy suppliers that they must implement the price cap properly and do their due diligence.
"It also shows that, where appropriate, Ofgem is prepared to work with suppliers that fail to comply with our rules."
The regulator said all 10 suppliers have since updated their systems and processes to prevent the issue from happening again.
Under the latest Ofgem price cap, an average household would face an annual energy bill of £1,738.
The issue has now been resolved with affected customers receiving appropriate compensation for the overcharging that occurred over the five-year period.
The regulator continues to work with energy companies to improve billing accuracy and customer service standards
PixabayThe error highlights the complexity of billing for properties with multiple electricity meters.
Customers who believe they may have been affected but haven't been contacted should reach out to their supplier directly.
This case demonstrates Ofgem's ongoing monitoring of energy suppliers to ensure compliance with price cap regulations.
The regulator continues to work with energy companies to improve billing accuracy and customer service standards.
With energy costs remaining a significant concern for households, accurate billing remains a priority for both consumers and the regulator.
