Ofgem said it had been assured by E.ON that all of the consumers affected had been identified and would be contacted and sent a rebate of an average of £14.83.
The amount includes 8% interest on the amount they were incorrectly charged.
More top news
There will be lighter winds for all of us than yesterday, although it will still feel cool.
Senior fashion analyst at Mintel Tamara Sender said: "For the first time ever sales of trainers have overtaken high heels."
Of the 1,600 business leaders questioned, a third planned to scale back hiring staff if the £7.20 an hour rate for adults increases.