Incorrect Billing

This is unacceptable, I am being billed incorrectly from MTN again and it seems as if nobody in MTN is capable of resolving the issue. I have a top up contract and I am being billed for more than the subscription amount on data and phone usage. It is a top up once my airtime and allocated data for the subscription I have to load airtime to use these services again, that is how a top up works. The customer service agent still says I am being charged for phone usage and data as if my contract is on a normal open line service. I don't even receive my monthly invoices for this account.