Telkom data contract ****!!!

I took out a month to month contract with Telkom for data and missed 1 months payment in December. They cut my data mid Jan, fine. Now when I go there to cancel today (14 Feb) I'm told that I must pay for Feb and March also including missed payment fees!! My question is how can I be charged for data that has been cancelled. To make matters worse the consultant at N1 City says the amount with keep on accumulating forever until I pay!!! What sense does this make??? What is the point of a month to month contract if you are billed forever regardless of whether you're connected or not????