Bad service. ******

I have a contract with cell c, *** in January I noticed that I was overcharged for data that they claim I used. For what I know is that I signed for a limited data with them. How can they charge me for unlimited data while I dnt have such contract with them. Now I have been trying to call them and sending them emails since March but I am not assisted. I stopped paying because I felt that I'm treated unfairly while I am a paying customer. Last month they send my account to debt collectors and they called me, which I requested a statement because I never missed a payment but only stopped paying because of the extra charges that I did not know where they come from. The debt collectors never called me back even today. Now you have tarnished my name to credit review. I know two people that you have done the same to, is that how you rob us our hard earned money.