Unsatisfactory service of MTN

I got a call back from MTN but i’m not happy with their response because they are telling me i payed less for April month which is R1355.77 but they charged me to amounts which are on my bank statement for 2 month which are April R622.27 and in May they charged me R699.00 so i still don’t understand what is going on. The consultant i spoke to said they were charging me month to month as my contract is finished so now they are sendimg me treats of discontinuing my service with MTN. I really don’t appreciate what the service provider is doing to me.