npower

I have been with NPower since 2016 but after the frustration felt by the inadequate ability to charge the right amount form my meter readings I moved to another supplier. Only to find that I was charged whopping 557 pounds which I owe them. When I called them to explain how this could be from my previous meter reading, It was explained to me that when ever you close the account a review of your time with the supplier is carried from the time you were with them so any tariff changes can be accounted. So this means that I owed 557. Why not charge as your going along, so that you do not get any unjustifiable suprises like this. Just to rub salt on this NPower said is that OFGEM has so enforced this on all suppliers to do!. Surely it would make more sense to charge what is owed at the time of payment and not get a surprise of your life when you move to another supplier to save money. Why not change this practice! How can you save money if your account is recalled since you started? Confused , and Frustrated.