Excessive data Bills

I entered into a contract with MTN last year, August. Since then, I have had bills in excess of what i am supposed to pay. Their answer is ALWAYS that I have exceeded my data for the month. I never received an invoice sincethe contract started. Last moth, instead of approxiamtely 250. 00 that should have been deducted from my account, an attempt was made to deduct approx 1400 from my account. Obviously this was rejected by my bank. I went into the MTN at canal walk and was promised that the problem will be escalated. Well, until today I have not received ANY feedback! It is almost time for the new bill, and nothing yet. I am not prepared to pay the bill of last month, as I believe I did not use date to the value of R1000.00. It is IMPOSSIBILE. I should have taken my business elsewhere. The worst service ever!