MTN's is being ********* and inconsistent!

I have 2 MTN accounts - one a data contract (2GB) and another a prepaid contract. I recieved my MTN data bill for this month and was utterly surprised to see that it was around R 2800!!! I have a budget and therefore i have alway had a limit on my bill. After 10 months of having a set bill for that account of R 99 I do not understand how this is possible. Usually, after i reach my 2GB's i am not allowed to go onto the internet. On all my prior bills the statement says i have a credit limit of R 500. Suddenly on this bill the credit limit has been changed to R 7839. Who authorised such a change? Where did the figure come from?<br> <br> I refute the charges and require a full investigation. I have been a loyal customer to MTN, only ever been an MTN customer and they have been my service provider of choice for all these years. To make matters worse their call centre is down --- strikes! So i am left as a consumer with a bill that i refute, debit order going out soon and no way to contact MTN except taking leave from work and going into a branch.