Incorrect Billing with no response from MTN

extremely frustrated customer, I upgraded my contact to a talk 100 @ R499 per month inclusive of VAT and added a 1 GB data bundle at R130 per month, we should only be billed for R650 per month yet our billing for FEB, March and now April is almost R 1000, which is unacceptable, we constantly call 808, will no success queries are made but no resolution and no one gets back to us, eventually we go into Fourways where it was opened they take copies of our contract and our billing and tell us to follow up after a week, when we do so we are told they have lost the copies and forgot to submit it we need to come in again, we go in again and the manager says she cant help and we need to phone head office, we phone head office and wait 20 mins on the line with no answer, Fourwyas manager says she cant help WE NEED TO GO INTO HEAD OFFICE and sort it out with them, this is totally unacceptable that we have to take yet more time out of our busy day to sort out MTN