******** deduction

I have 2 cell phone and 1 modem ( 500mb) Contract with MTN. Normally the cost for all three contracts are R645.00. Note that this is a debit order. So they deduct what you use. My bill for December 2015 was R637 and for January 2016, R645. The 2 cell phones are top up contracts, and the modem is 500mb only. In February MTN tried to withdraw R3907. From my account, but it did not go through. In March R5200. I have asked them to look into this account and requested a URL , but no one is coming back to me. I have also told them that I am going to pay the 2 cell phones only, until this matter is resolved, which I did, but they still disconnected the cell phones. Can anyone advice me on what to do.