when you TOS a prepaid line, why would you expect a customer to pay for it?

I have used Telkom's adsl for over 8 years, i have also paid for services before i use them because adsl billing states that i am billed for the coming month. I short paid my bill for a month and Telkom suspended the line because of the shortage in payment. Telkom then asks me to pay for the suspension and also the charges for the same month. I told them, NO, it is a prepayment. You take your service means i do not get the service. What do you want me to pay for a service you never rendered for? I told Telkom, i will not be taken for such a ride and i cancel because the contract had ended and Telkom was then on a month to month basis. I specifically told them i did not need their services anymore. Telkom cancels when it likes and no wants me to pay for the time it took them to cancel. Can someone please think this out logically? We are not robots please.