said by MediacomChad:Unfortunately we do not have a way to monitor what programs or devices are using the most. You may want to check in your router for any connected devices that you don't recognize. It's possible someone has made their way into your wireless network and started downloading things.
Out of curiosity, even if you can't monitor which programs or devices are using the most, you would in theory be able to break it down day by day right? Hour by hour? Then the OP could at least compare that data with the hours he knows the Xboxes are in use.
Herein lies exactly the problems people are afraid of when it comes to caps. It's downright difficult to track all bandwidth usage at the router end, at least with some older models of router. You can custom flash them with firmware, but that's not something all of us are comfortable doing. So in the end, we're stuck just trusting that the ISP is measuring correctly, and we really have no way to verify that. Unlike the water or electric company, there's no oversight to make sure that things are being measured accurately.