Mobile phone provider sent me a bill for £245 of "data charges", they're refusing to investigate and order that I pay right away. Bullsh*t!
Mine did that to me, I refused to pay for it cos 1.5gb of data used isn't worth $400, they were really rude when I told them I was going to go to the telecommunications ombudsman. Went to the ombudsman, out of my contract, no exit fees, didn't have to pay the debts that I had incurred and my phone which was part of the plan was given to me outright.
Call the authorities, they always will help out the little guy.
Check the contract you signed, if it doesn't give a specific amount that they will charge you per extra KB over your data allowance then you will be fine.