Dont keep their end of contract then want to charge for their mistake

I rented a adsl line from telkom, after numerous attemps to get proper speed i ended canceling ALL services. I did the cancelation via fax i have fax report as proof and i did it online via self service, i received email that cancellation was received. As per contract notice is 20 working day. I received notice october, november 3 days before service was supposed to end i phone telkom to confirm everything was running smoothly (line was dead anyway) and i received account that charged me past the time frame which service end was due. Operator confirmed cancelation is registered and that it will end on correct date. Also informed me that statementa went out before and that the next month starement would show die credited amount. I said i would wait for correct statement. Next month came and again i was charge for an additional month service past end date. Phone again email proof, this continues for the next month again same story. Service still not canceled get charged again (by the way line and everything was disconnected and not in use from my side) finally in january i get it cancelled, dispute gets registered never hear back from them ever. Next thing i get phoned by lawyers i was handed over. Send proof to them only after months get phone again by someone else, repeat same process. Now im handed over to debt collectors for money i dont owe and for i mistake that was not mine. They costed me money phoneing endlessly to try and fix their mistake and bad service