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 Duke of Cambridge said his children were beginning a "lifetime of friendship" with Canada as they began their tour of the country.
When and where are they on, and how do they work?
What better, more dramatic spectacle has there ever been on American television?