Overcharged on monthly bill

Over the last two months, I've been debited over R 10 000 for a cellphone contract and data package. It began in July when I was billed R 4677.55 and now in August I've been charged R 5696.07. Over the years that I've been with Autopage, my bill has averaged R 1 100. In reviewing the itemised billing, the most charge is on data. I am on a package of 2G per month at a fixed price of R 250. My call charges average R 230. How does my bill get to these ridiculous amounts? What's worse is that I use the data to send e-mails and play chess online. For these activities, 2G is more than enough. At work, I use the University's internet services. I don't run a business. I am cancelling all my contracts with this company. But first, I need my money back, I am not able to meet other commitments because of me being overcharged.