Day light *******

I had a cellphone contract with Cell C about a year ago. I paid it off and called them to cancel sometime in October 2014 as I did not wish to renew it. Since then they have been billing my account with amounts less than R100 per month ( as these do not report in my phone when debited), sometimes twice a month. I called them at the beginning of 2015 begging them to stop this billing as I did not have a cellphone contract with them. Each time it was a promise that they would eventually stop and pay me back the money they had been billing from me. But to this day 02 July 2015, this has not stopped. On some months I take a trip to the bank to reverse these payments but it costs me money to even reverse each payment, thus leaving me still on square one as they use different reference numbers to debit. I do not use a Cell C number, I do not owe them for any service and I do not have an contract with them, but they are debiting every month from my account. In June they have even debited twice. I am taking legal action as I cannot be held hostage by a company I do not owe a dime!!!!!