Amount debited tripple what the invoice says

My same account A ********** which I have been complaining about is still having billing problems. My bill was finally fixed and now has no insurance premiums as was before, but now the amount being debited is not the figure shown on the invoice/bill. The invoice amount due in December is R471.45 but the SMS says R1151.78 is being debited! WHAT THE HELL IS REALLY GOING ON WITH MTN, WHAT IS THE POINT OF SENDING ME AN INVOICE THEN IF YOU DECIDE TO CHARGE ME AS YOU PLEASE!!!