Late Cancellation

I had a 24 month contract with Cell C which expired in October 2015 since then I am still billed for something I don't make use of. With the delivery of the phone Cell C provided me with a sim card I have contacted them and explained that I will not be using their sim and therefore stay with my old contact number which was agreed when I contacted them asking why there are still money being deducted from my account I was told that I receive data bundles so I have sent numerous emails to the retentions and customer service departments for my account to be cancelled and I even called to confirm whether the account will be cancelled in October of which was confirmed so how can one cancel a contract but you are still billed for data bundles you are not even using. Cell C is a very *********** company and it is as if the call centre agents are only there to answer the calls but are doing nothing not sure how or when this will be sorted out.