npower sent me an estimated bill, to be paid by direct debit
They also sent a letter saying I needed to read my meter, in order for them to check if I was on the best tariff. I did, although I admit I did it rather belatedly (partly becuase they wanted me to read it once in the morning preferably after 9am and once in the evening before 9pm. As I leave for work at 7.45am, and haven't been home at weekends for months, the former was tricky. In the end I had to read it when I could and send an explanatory note)
Anyway, having sent this info in, they sent an "amended bill" about a month later (for half the amount - yay!).
They've taken both amounts...
So now I have to badger them...