Bad Service

I had a data sim that was month to month. So the month finished and I do not want to carry on. Cell C try to deduct the money from my bank account which I did not give to them and so the d/o did not go through. Now I need to pay R70 per month for a d/o that was not sign for and did not even go to my bank. There were no trace of that and monthly installments. I've asked for statements from credit controllers, from Cell C customer care, Cell C creditors and still nothing for 2 years know and they still keeps on harassing me for payments. I have sent numerous mails, answered numerous calls and every time ask for statements but still nothing. What do I need to do. Know my ongoing contract that is up to date with a d/o that is up to date is due for renewal and know they have a problem with the renewal on that account. I don't know where to go to or what to do to get a statement to see what I need to pay on the "outstanding" number that I also do not have anymore. Cell C blacklisted me for this account but still nothing from there side.