Hello irondolphin - welcome to the forums... thanks for joining
Sorry to hear that you're having issues with Orange. I have read similar posts to yours, but never heard of a bill being so high!
I'm guessing you haven't been using your phone to tether a computer and that Orange are saying that this is all mobile data?
I'm pretty sure they can't tell you what you've downloaded, but would have thought that they should be able to give you a breakdown of when the data was used? I'd also ask why they didn't cap the bill/contact you to tell you that your data usage was excessive... over