I always wondered how I could use my data so quickly when I used my service. Well truth be told. My buddy and I changed services providers 1 year ago and rather than pay the early termination fees we downgraded to lowest plan and just unplugged the router.
IMAGINE THIS EVERY MONTH I USE 100% OF PRIMARY DATA AND 70% OF BONUS ZONE
If you only plug in briefly it will never have time to update the totals. It's showing what it was back when you first unplugged it.
As BirdDog alluded to, the data can't reset if the modem isn't plugged in, and until that happens it will continue to appear as it did just prior to being unplugged. If you plug it back in and allow it a few minutes to communicate with HughesNet's servers, the data will reset.