incorrectly billed

I have a total of 3 contracts with MTN and all of them is set to 0 billing yet this month a debit went off by R500 extra when calling the call center they advised that one of the contracts went over their given min or date amount <br> and that the payment is correct. We then went into mtn and the lady showed us the limits on the 3 contracts is still in tact and that she cant see how the accounts was billed extra. we then called the billing department today and they advised it can take up to 7 working days for the matter to be resolved this wrong we didnt make the mistake of billing the account incorrectly why must i wait for my own money and why is there a limit set if mtn cant assure you that what you signed for is going to happen. MTN is by far the worst company to deal with even cell c is better when it comes to resolving queries especially ones where money is involved one thing is for sure mtn will not be seeing me again this is my last time renewing my contracts and i will spread the word of the ****ty service i have been receiving.from a very unhappy customer