Paying for your error!

Since renewing my contract almost two years ago, my average bill has been about R650 per month. I am very careful with data ans as soon as I see my data is almost up, I top up with a gig bundle. This month, I get debited close on R4 000 - most of it being data charges. I check regularly with *141# to ensure I have not used all my data, and there was always data there. Now they are telling me I used over R3 000 in data? I would happily pay bundle rates but am not going to be conned to the tune of R3 000 odd on data. I never picked up this charge on my bill as that is emailed to me and, would you believe it (incompetence again on your side) it was *******ed. I didn't worry because I was confident it would be my normal amount. I have reported this online (***), but not a word from Mtn. I have also been charged for sms's - of which I have 200 free on my package and only sent 66? What the hell is going on MTN???