Sarah Harrison, Ofgem's senior partner in charge of enforcement, said:
Ofgem has put in place protections for consumers so they can get a fair warning if their supplier puts up prices and time to shop around for a better deal.
E.On has accepted it failed to meet these protections. Today's announcement that E.On will compensate customers is a positive step by the company to put right their mistakes and is welcome.
More top news
The cloudy skies will remain across the UK for the next few days before the week ends with temperatures as high as 14C.
Polish migrant workers living in Southampton say they believe cutting benefits to people like them would be illegal.
A young woman has given ITV News a glimpse of what it's like to live under the rule of Islamic State in Syria's northern city of Raqqa.