Data consumption

When i renewed my cellphone contract in 2014. I told the consultant to please make sure that there is a ceiling on the amount of airtime I can spend and the amount of data I can use. I always had the ceiling and I buy additional prepaid airtime when theirs is depleted. A month ago I realised that i could not make outgoing calls. I called MTN to find out why and I was told I had used exorbitant amounts of data so they blocked my calls and i could not even use the data or aitime I had purchased. This came as a shock to me as I had told them that i only require a certain amount from them and no more than that. I asked to speak to someone who could open my line again, held on for 30min or more. Eventually I was told it would be open by the following morning. This did not happen, so I had to call back 2 or 3 days in a row to fix this problem.The line was eventually open, I was not however told that there would be additional costs that I would be charged, I was told that they would conduct an investigation and come back to me. I have not heard from MTN since. I was charged R855.10 in August and R1618.01 instead of the normal R500 agreed upon.