Billed for Insurance that I do not have.

I have a contract with MTN and I signed up to pay R779 however due to interest rate going up my contract is not R785. I have been receiving statements of R892 and R890 for the past two months, I went to query with MTN because my statement says the amount is for "cellphone insurance" , I have never taken insurance for my phone and I am not getting assistance. I went to MTN in La Lucia and MTN at Musgrave Center no one assisted me. The call centre is worse and the insurance call center just doesnt know what they are doing. I want my credit now and they must stop sending messages that i owe them. The service from MTN is ridiculous.