Sudden crazy data usage - what went wrong?

When I was out today, I opened safari only to get a message that I had run out of data and need to top up (Three UK). The last time I checked a week ago, I had 1.5gb left out of my 3 gb allowance. So, I checked my usage and was shocked to see that I had used 9.5 gb of data! My limit is 3 gb so that can't be accurate and, yes, I did reset the statistics when I topped up last time.

I'm thinking about what I've done over the past week:

browsing with wifi
youtube with wifi
email over 3g
safari general browsing over 3g

I can't think of anything else.

What's going on? Even if the ipad usage stats are wrong, I don't know how I could have used the remaining 1.5gb in just a week. I usually use less than 1gb per month, often not more than 800mb or so.

Any thoughts?

 

I've never experienced any data use like this in the 6 months I've had the ipad, so I doubt very much it has anything to do with email. Besides, 99.9% of my email are simple text messages without attachments. They wouldn't add up to this kind of data usage.

Maybe some rogue app? Hmm...need to figure it out so I don't immediately use up my quota next time.