I see a lot of DoS attacks that my router drops the data on. Your staff has confirmed they see a lot of triffic at the same time (1 am - 5 am), what I want to know am I being charged for this data and why are DoS attacks not being stopped and not propagated down to me?
ISPs can only mitigate DoS attacks, complete prevention isn't really possibe since more sopisticated attacks can resemble legitimate traffic. I'm certain ViaSat has some mitigation in place - but anything that seems like it's legitimate and makes it's way to your router would likely count towards your data usage - I often wonder myself if these arent the source of excessive/phantom data usage.
Best you can do is ensure your own protection - go over to ShieldsUp! and see if they pick up any vulnerabilities (they offer suggestions for any found).
Might agree if my basic netgear wasn't dropping the traffic by default. Annoys me that I would have this counted towards my data usage, especially since it only appears to be happen during overnight hours.