I'm really fed up

I have 2 contracts with MTN one for R459 and the other for R529 and since November last year an amount of R1128 has been debited from my account instead of the initial R988. I have called MTN twice and each time I am given reference numbers and assurances from the consultants that the error will be fixed. Earlier in the month I again called MTN and was assured that the matter will be handed over to the supervisor since it was not the first time it was happening. With such a response, I expected the correct amount to be debited, but to my annoyance again R1128 was debited. I am running out of patience with MTN because the excess R140 that is being deducted i can use for something else. is this matter such rocket science that two consultants later it still cannot be fixed?