The community can probably help you figure it out, but you will need to follow this procedure first: https://community.hughesnet.com/t5/Tech-Support/Where-s-my-bytes-Testing-for-data-leaks/m-p/77194#M5...
I wish somebody can tell me how I lost 8.4 gigs in one day when nobody is home
One or more devices almost assuredly used it, though without you being aware of it. The following two posts are a good place to start to learn how to lock down your devices to use as little data as possible without your say so.
If these don't help, let us know what devices you use with HughesNet and we can help steer you in the right direction concerning what to do. Just in case, you can see all currently connected and disconnected devices here. It shows everything that has connected directly to the HughesNet modem since the last time the modem was plugged in, whether via LAN or WiFi.
Lastly, if you have a satellite TV receiver connected to your HughesNet service, it'd be a good idea to disconnect it, as there is no way to control the amount of data they use, and they can use it for more than just on demand viewing.