keep debitting without authority

Each month cell c debits more than a R1000 from my account. The amount varies as it becomes more each month. Yet the contract ended feb this year. The sim card has been inactive for months as cell c refused to do a sim swap as there was apparently R147 outstanding. Which I paid, R150. this amount never came off. I am not receiving airtime, nobody bothers to call me, which I requested months ago. If the account is in arrears, what is this money for and where is the airtime? Why has the agent to date not returned my call after telling me there is no amount outstanding on the account when I asked for an upgrade. What is going on at cell c! This is the 100th time I am having issues with cell c. The service is atrocious.I cannot see why the directors of this company are not putting measures into place to streamline the processes. Customers are given incorrect information, info doesn't get updated, we are held liable for cell c's errors, there is no feedback, calls are dropped, the list goes on. I get great service at Vodacom for much better rates. I need an agent who can give me proper info, to call me. If my account is debited again I will be laying a charge of theft.