The energy supplier has also agreed to make a £300,000 goodwill payment to a consumer fund it runs in partnership with Age UK.
Under licence conditions which Eon breached, suppliers have to give consumers 30 days notice period of a price rise. If the customer arranges to move before the increase takes place they should not incur an exit fee or the higher charges, even if the switch takes place after the price rise.
All of the consumers affected have now been identified and should receive an average rebate of £14.83 in January.
Sarah Harrison, Ofgem’s senior partner in charge of enforcement, said: “Today’s announcement that Eon will compensate customers is a positive step by the company to put right their mistakes and is welcome.”
David Bird, customer service director at Eon UK said: “We are very sorry to have let down some of our former customers and have made clear that we will refund the money plus interest. Our systems are being updated to ensure this mistake can never happen again.”