Excessive Data Bill

I've been charged over R7500 for data usage, when I phoned to query I was asked to fill in a URL form, I'm still waiting for a response as I'm wanting to see the data usage. This was done on the 7th May, after getting two reference numbers I'm still waiting. I switched the tablet off on the 8th and got another bill for data usage, I have now suspended my contract until matter has been sorted, I still have to pay contract fee but I'm now losing 500MB per month. I'm wanting to sort this out soonest, who has that type of money for data?