Cancelled contract now contract still active

So a couple monts ago my debit order was cancelled by vodacom without me knowing. 3 months later i get a call saying im in behind on payment. (Note havent used thr contract because tablet broke and only had the contract for the tablet) so i payed the areas and cancelled the contract. Now they send me a bil for two months again saying that i must pay this and then cancel the contrct again and that i dont i will get charge each month again for the full month??? Sorry but isn't a contract not valid anymore asoon as one of the parties does not keep the commitment. My 24 months are over and now you want more money. Im paying for a service that i dont even get or use? On this day one of there guys phoned me but the did not understand and i told im n couple of times that im sorry because its not his fault. You guys are draining the little guys financial. I don't have the money to pay the extra 2months now and next thing im going to get a summons get a judgement and then R700 becomes a couple of thousand. Actually bad because was a loyal customer for years and cant see how after this that i can ever feel the same about your service.