Shell Energy is to refund more than £500,000 to prepayment customers it has overcharged for gas and electricity in the last three years.
Ofgem confirmed that the business will be forced to return £106,000, as well as make good will payments of £30,970 to the 11,275 affected default tariff households.
This comes as the energy regulator are to announce a new energy price cap tomorrow morning, raising the average gas and electricity bill from just under £2,000 up to £3500 annually.