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
Six teenagers had a lucky escape after almost getting cut off by the sea while searching for Pokemon Go characters.
Clinton needs to win over doubters all over the USA. We joined a family of sceptical and divided voters to see if her message hit home.
An ultra marathon runner found the perfect running mate as he competed in the 4 Desert race in the unlikely form of a stray dog.