BILLING/CALL CENTRE

I have a 3G account with MTN. This was through Nashua Mobile and for the last 3 years i never not once had an issue with being over billed. When Nashua handed to contract to MTN, my world just fell apart. where i would pay R 99 for the 2G per month, and i had set a limit on the account, i have now been billed for close to R 7000. 1st months billing went off as normal, second month went off as normal, 3rd month no payment because then i received a bill for almost R 2000, obviously this was not accommodated and when i tried to call the call center there was no helps at all, because i held on for an hour. So i left the account unpaid, the 3G was then blocked, shortly there after i receive a bill for R 1500, Bare in mind i am not able to make use of the device as it is BLOCKED. I want to know who at MTN is using this account when it is clearly been blocked, over and above MTN has now listed me on ITC. Yesterday i received an SMS stating i owe them R 6936.78, Telling me to pay, NOW I ASK, IF YOU CAN SMS ME, WHY CAN'T YOU CALL ME MORE IMPORTANTLY, WHY CAN'T I GET HOLD OF MTN. I need to speak to someone regarding this account and the call center is of no help. Absolutely disgusted.