MTN rely on vague conversations to ***** thousands in data

I added a usage limit so that I could roam and make international calls. I didn't know that this usage limit would simply be clawed into once I reached the capped amount of my contract. Now to try and dispute R12,000 of data is proving ridiculously difficult. I have called several times to follow up on the calls that are being extracted so that I can hear where I agreed to this (perhaps I am mistaken, but I find it hard to believe that I would agree to incurring R6,000 per month on additional data costs). Not only don't they respond, but the calls get ended as I'm starting to follow up, the supervisor was promised to phone me back two weeks ago and nothing since then. Once this contract is over I will never support MTN ever again, so much for a client of 17 years.