Within the past month or so I started noticing high data usage for seemingly no reason at a rate close to twice to three times that of 'normal' (Read: There's absolutely no reason for simple texts to use tens of MBs of data). The only common link was that it appeared to be coming from the iPhones that both my wife and I use. These are usually updated promptly whenever apps and new iOS software is released.
If you too are having high usage, it could be one of the iOS 11 updates that 'fixed' one wifi problem, yet caused another in the process. 'Forgetting' the wifi networks associated with your modem, rebooting the phone, then re-entering the network information may be a way to erradicate part of this problem:
1. From Settings go to Wi-Fi.
2. Get the info of any currently used or other network listed by touching the blue i in a circle.
3. Jot down the settings for this network connection - you may need it again later in step 10.
4. Kill the network by touching 'Forget this Network'.
5. Repeat steps 2 thru 4 for any 2.4GHz or 5GHz wifi settings you might be using with the HughesNet modem.
6. When done killing the network connections, go back to the main Settings, and toggle Wi-Fi Off.
7. Hold down the power button until you see "Slide to Power Off", and slide it. 8. Wait about a minute for the phone to power down, then hold the power button down until the phone reboots.
9. Once the phone is rebooted (you may have to entered your 8-digit passcode first), go back to Settings -> Wi-Fi.
10. Re-enter the networks you took note of in step 3.
Hopefully after going through all this you too will see data usage return to a more reasonable rate.
* Disclaimer: I am a HughesNet customer and not a HughesNet employee. All of my comments are my own and do not necessarily represent HughesNet in any way.