why is my dish satellite data usage so high all of a sudden.?

I have the 15 meg data package with Dish Satellite ISP. Very high. The past 4 months I haven't even gotten close to that limit. Now, 3 days into a new billing cycle, they tell me all of my data is used up. They can't tell me how it got used up, only that I've hit the cap.
1) Is there anything I can do. I think they've made a mistake measuring my data. They say that's impossible and my only option is to buy more data.
2) Is there some way I can check and see what is using up all of this data (my wireless is secured with a password)?