Unexplained data billing

I have a huge problem with Vodacom (data contract taken at DD Campus) that keep on debiting my bank account an amount of about R7600.00 every month for data usage that they can't say what was it for. What make this worse is that when i took the contract i clearly requested that they put a limit to both my voice and data lines and this was done only on the voice line. Then i got a billing of about R858,00 after that it was R1348 of which i reversed. Then it escalated to R6341. I logged a call (R Ref# A1-X20P-PD61HS) with Vodacom requesting itemized billing which states exactly what is that i was using so much data on and i could not get any feedback. I also requested the staff at vodashop DD to help with the call i logged and that was in July but i have NOT had any feedback from them either, I followed up 2 weeks ago and still no feedback. I have always taken 2 gig and that is data i have never finished in a given month, so all of a sudden i finish my data and getting charged this exorbitant amounts and when i want to know what is i have been using this data on, the silence is deafening from my service provider and that is the service one gets for being a Vodacom customer