Account not properly billed

I upgraded my cellphone contract on 3/07/2015.I specifically told the consultant to set a limit on my data and call charges,During the upgrade process,whilst my phone was being set up,the data charges went over the limit and I was billed by MTN About R644<br> They claim that the R644 was the previous months account/bill which is not possible because I used to pay R449 per month on the previous contract.<br> The consultant claims that he has consulted the customer care/ accounts department and there is still no feedback from them,and it has been over 2 months.<br> My bank account was debited that amount,plus the current