Same thing happened to me, I got a warning on my phone saying I was about to go over my data usage which I thought was strange, and saw that something used almost 1 GB of data in a little over two hours. I was at home on WIFI when it started. I called customer support but they could not help me out.
Data overages can be very alarming. I can certainly understand wanting to make sure this does not happen again. Let's get this resolved. Did you completed a price plan change recently? If you completed a recent price plan change your data usage may have been prorated http://bit.ly/xB4iTc . Any applications downloaded count against your data usage. You can go to settings >general>usage> storage, to see how much data each application would have used to download. You click on cellular usage in the same usage screen, and it show how cellular data that your device has used. Keep me posted.
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