Huge MTN data bill

I have been on 3G contract for years now and I have paid R500 at most. I only paid R1500 and R1800 for two months in June and July when internet was down at work for 2 months because of renovations and my boss asked me to use my 3G for work.<br> <br> To my big surprise this October month I receive a bill for R2700 used in one month when I have a 1 GB a month contract since February from 500Mb contract previously.. I do not see how my bill can jump from a consistent R69 a month for personal use to R2700 in just one month. <br> <br> I was under the impression that the data is depleted first before it starts charging out of bundle rates. How have I been paying R69 a month consistently before this.<br> <br> I am very dissapointed at MTN. The itemised billing does not even show when the data was depleted and what exactly is it the are charging for. To make it even worse all R2300 of the charges were on the same day.<br> <br> It does not make any kind of sense.