R79 account goes to R5000 without extra usage

We have 3 accounts with MTN one which is a Laptop on a R79-00 per month use your own special. The past six months the billvaried between R79-00 and R200 as we do not often use the Laptop. This Month we got a bill of R5000. We did not download anything and used the laptop the same as every month. I logged a query on mail and got a response that the R5000 is valid from Rabelani Tshivhase. This off course not possible and there is some serious issues on the go at MTN. I cannot get through to the customer care ***, cant get through to the head office switch board ***, and also this number ***. This is very frustrating that I have to pay R5000 which I certainly did not get the value for. Please help Is there anyone that can assist me in getting through to MTN.