Mtn billing errors

Hello Peter my name is Xoli please help me out l have a problem with the mtn billing system they are overcharging me every month and its been happening for three months now. I have spoken to them each and every time they bill me but they don't want to sort this thing. I am supposed to pay R1.248.00 but they always bill me above that around R2,800.00 or R1,800.00 and when I address this issue with them they always say they will escalate the matter to the billing department. Please advise and help.