Incorrect Billing

I have recently complained about MTN suspending my services without notice, they responded and indicated that I have recently upgraded my contract which the subscription is R499.00 pm yet MTN for the past 2 months and this month, were or will debit my account in excess of the amount agreed between me and the service provider. I have tried numerous times to contact the service provider but have failed constantly to get hold of them, when I visit one of their walk-in centres, I am told to contact 808. I am failing to understand why I am billed these amounts as the contract that i signed up for is a top up, and I clearly stated that I want a top up and nothing else. Currently I load my own airtime and own data if I run out of any of these bundles yet I am charged. I fail to understand what I am charged for and now this is beyond what I have budgeted for. <br> My billing periods for the past 3 months are: <br> April: R814,58<br> May: R718,44<br> June: R727.42 Which i don not understand where MTN gets these figures.