Data billing

We keep getting high data charges, all Mtn says is it's valid and the charges went up from 1 April, how can charges just rise to 300% our unbilled data charge is again over R5000 I bought 2.5 gig via Fnb and havend even used the data card for 2 weeks, the sim isn't even in the card, we have a R12000 credit limit which we lifted to R15000 when we were suspended and received over R38000 account how is it possible, Mtn schweizer placed a block of R1 on our data acc the 16/7/2015 after telling me it keeps running but it wasn't connected or in divise 16/17 of July, we weren't home I remove it since our high bills started! For 2 weeks the sim isn't even in device how can billing charges keep running! What is going on! Please suspend all data cards cause your bills just don't stop running away, Mtn sr can't suspend data cards because we cancelled debit order we would like to pay you what we owe and used, but not these data charges its ubsurd, why do we have a credit limit, we will only pay up to our credit limit, please credit the rest so that we can proceed payment and cancel all data cards.