An electricity bill and green household brands

This morning a bill arrived from my energy supplier, whose name is e.on. The bill showed that e.on owe me £240.21 because I have over paid. e.on seems unable to estimate my bills fairly; they always take too much money and trying to get the money back from them is not an easy or straightforward experience. Last time it took several telephone calls and a meter reading. They did not make it easy.