Payment collection

Am not happy with their payment collection system, I have cancelled my services because am no longer working. With my understanding that we pay upfront for services only to find out that is not like that, I have an outstanding payment of previous services used which I dont understand but I end up agreeing to make the payment when I get money, but now they keep on collecting money in my account every day which has zero balance and now is affecting me badly with bank charges, I tried to explain to them with no luck saying that they will keep on collecting every day until i make payment, that's how their systems works as they explained, the consultant was even rude to me questioning me that: what am saying meaning they have to do that to all their customers