You can pay like that if you want, you'll just lose the direct debit discount (was £30 per fuel last time I checked)Why does it not function like this… Use goods get bill at the end of the month, pay bill, use more goods and get next bill at the end of the month.
Why do they insist on building up credit with them. It seems like they are almost treating it like a prepayment meter.
Most people pay a bit more in the Summer to cover the extra cost in Winter, saves getting a massive bill in January for example but there are other ways of paying if you don't want to do that. Or at least there used to be, haven't checked recently.