MTN's ********** billing practice

I am an MTN cellphone contract holder. My service was suspended last week after I was informed by sms that I had exceeded my data usage credit (the sms just said 'credit limit'). I do not use the phone for internet except occasional brief google searches, and I want to dispute the usage. I have been to 3 MTN shops and they insist I must phone the MTN helpline on 80800 to lodge the complaint. I have now phoned more than 10 times and am always cut off while holding after 1 minute and 4 seconds. <br> In the meantime my service remains suspended, and I view this to be a breach of the contract. I refuse to pay the data usage fee and am being denied an opportunity to have it corrected. I do not recall ever signing for a data usage credit limit (and if I did, this was definitely never explained to me - I do not need it, have internet at home, and also would never want such a limit that can run up into thousands of Rands without my knowledge). Furthermore, why does MTN allow me to run up R 4 000 worth of credit and not warn me as soon as I go into credit? I refuse to pay this amount. A former colleague sits on the National Consumer Tribunal and will be my next port of call.