Unauthorized transaction

Cell C have been deducting funds from my bank account without my authorization , I called the scall centre no one could help. I went to a store where I was told that they will need my bank statement, ID and affidavit from the police station of which I supp**** and till to date I haven’t received any response. Today an amount of R2300 went off my account again, and all they say is someone took a contract with my details. What I want to know is how can this be stopped because it’s been going on and I’m not receiving any assistant.??