MTN no help

We did a upgrade in December 2014, we ask the consultant for a top up 100 and we explain to him that the debit order must be the same every month because we earn salaries and cannot afford a open contract. In May 2015 we discovered that MTN had debited the account with almost R5000.00 and our debit orders could not go off. No the account is standing on ?R6000.00 and we had to stop the debit order . We still pay every month the contracts but since MAY 2015 we are struggling to get answers from MTN and it is impossible to phone them. The phones have been blocked!!!. <br> <br> They say we have no proof of getting a top up 100 and we did not set the limit, but we made it very clear to them we want a top up 100 with the same amount every month.<br> <br> How can one take out contract that will cost you almost half of your salary per month does not make sense to me.<br> <br> I need some response please!