UK energy supplier E.On has agreed to pay a further £7.75m in fines for overcharging its customers, industry regulator Ofgem confirmed on Thursday.In November 2012, E.On paid a £1.7m penalty for a similar breach, although a spokesperson for the company claimed the "underlying cause" was different.Sarah Harrison, a senior partner in the enforcement arm of Ofgem, said the latest fine was slapped on E.On for "repeated failures.""It's absolutely unacceptable that E.On failed to provide vital customer protections yet again, and this persistent failure is the reason for the high penalty," she added.Ofgem said many customers were asked to pay too much in the process of switching while others were charged wrong exit fees. Around 48,000 customers, including 7,000 pre-payment customers, were potentially affected in the latest instance.The company has apologised for its failings and will pay the fine to the UK Citizens' Advice Bureau to help vulnerable consumers.