Mistake with contract cancellation cost client

I cancelled my contract with Cell C following the prosess they advised me to follow. After the call an agent called Musa assured me that my contract is cancelled and that I don not have to do anything else. My last billing will be for September 2014. It is now February 2015 and Cell C has ever since been deducting my monthly payment even after I personally cancelled the Debit order with my bank. I have spoken to 9 call centre agents ever since who have been transfering me from one department to another and each time I have to explain my story all over again and answer the security questions. Each of the calls cost me money. I have a reference number for the call where I cancelled my contract and all Cell C have to do is listen to the call. I received a case number In January 2015 and when I followed-up yesterday (16 February 2015) the case was closed according to their records. Do date I haven't received any feedback and Cell C just keeps charging me for a service I cancelled using the correct procedures.