Unexplained High Data Usage

I am a pensioner and have had a Vodacom 2GB Data contract for more than 3 years just for e-mail and a bit of Internet usage at home. The 2GB per month was always more than enough (this can be validated by my account history), however all of a sudden this month the 2GB ran out round about the 10th of the month, I bought another 2GB but yesterday, the 17th, it ran out again. Then I looked at my account and was shocked to find that it is already almost R3000, mainly due to out of bundle rates that were app****. I contacted the Call Centre but was greeted with a no sympathy attitude to my problem. According to the operator I used about 4GB on the 17th alone, which is impossible as I don't do any downloads (music, movies, games, etc) and we were not even home for a few hours and also had 4 hours of load shedding in the evening. The Call Center's operator's attitude was that I used it and will have to pay, however, I insist that I did nothing unusual and that somewhere something went wrong on Vodacoms system or ***** was committed and this matter should be investigated properly. As a pensioner I can't afford these extreme costs, especially as it is due to no wrong doing from my side.