MTN High Billing

I have 2 fully functional contracts with MTN,one data line and 1 voice. For 12months or so, my average usage for both the data line and the voice line have been similar, until July 2015 and August where the figures for data shot up.To my surprise, my usage in terms of behaviour has remained consistent. MTN will always send me sms notifications to alert me of my data depletion on my *** number. When the alert happens, I would naturally limit internet usage until I purchase data on the *141* number. I would then recharge for normally 1GB (also get free 1GB). I do that so that I don't browse the internet without having data bundles.My invoice amount for July and August totaled to +- R2384 and there was also a huge discrepancy between the amounts that are invoiced and the amount that show on the billing link which raises eyebrows. I have since consulted MTN to issue me with the line by line details of the charges and no response has been forthcoming even to date. I have committed to them that I will reverse the debits until the matter is settled & will only pay for normal charges. They have disconnected my line services and managed to threaten me with legal action.I need help.