This reply is kind of long, but it's addressing each of the issues you mentioned in your post. Each topic is separated.
With regard to the WiFi not staying connected, what happens with your devices when they have no other source for internet? What I mean is, if your WiFi on your phone is turned on, and your cell data is turned OFF, what happens with the WiFi? Does it stay connected? On the other devices are you actually seeing the WiFi connection being lost and the device having to then reconnect?
It's possible that there is some type of interference or just a bad signal. The reps can remotely test this, but they're normally not on in the evenings. One recommendation is, if you're using the 5Ghz signal, try using the 2.4Ghz signal. The range of the 2.4Ghz signal is much better.
Regarding the speed issue, the reps will need some speed test results. The instructions for the running the speed tests are here. Because the tests need to be run with a LAN cable connected device and with the WiFi in the HT2000W modem disabled, the WiFi issue won't be an issue for the speed tests, though that issue still needs to be addressed, of course. The speed tests should be run ONLY if you have data. If you are currently out of data and throttled, please wait until you again have data to run the tests.
Regarding the data loss, there is almost assuredly something still connected to your HughesNet service and using data that you aren't aware of. On this page you can see what is currently connected, and what was connected, but is no longer, since the last time the modem was plugged in.
To test whether any data is being used by the modem itself, there is a modem isolation test you can run. The instructions are as follows...
Please perform the following test outlined in the graphic below. This is known as a modem isolation test, and it will help to determine whether the issue is with HughesNet or your local network..
1: Disable the WiFi in the HT2000W modem.
2: Take a screen capture of the HughesNet Usage Meter, along with the clock on your computer screen.
3: Disconnect the LAN cable from the modem, noting the date and time of disconnect.
4: Leave the LAN cable disconnected from the modem for several hours. HughesNet recommends doing this overnight, or during the day while at work. DO NOT unplug the modem from the power. The modem must remain powered.
5: Reconnect the LAN cable to the modem, noting the date and time of reconnect.
6: Take a screen capture of the HughesNet Usage Meter, along with the clock displayed on your computer.
7: Post your screenshots to the community.
Please be aware that, if you downloaded any large files just prior to this test, some usage may appear to have occurred due to the slight delay in the modem reporting the data usage to the server, but it should be rather negligible.
If you don't know how to disable the WiFi in the HT2000W, please see "How do I manage my built-in WiFi modem?" in this PDF. Please be sure to click "Save Settings" after unchecking "SSID Enable" for each of the four tabs individually (2.4Ghz, then 2.4Ghz Guest, then 5Ghz, then 5Ghz Guest).
No doubt the reps will have to take a look at what's going on. I'll tag a couple, just to be sure they see this and reply. Though you can't run the modem isolation test without a LAN cable connectible device, you may still be able to run the speed tests to start troubleshooting the speed issue, but I'd wait to see what the reps have to say first, especially with the WiFi not staying properly connected.
In the meantime, if you haven't tried already, power cycling the modem might help with the WiFi issue. To do so, unplug the modem at either the wall outlet or the power pack, wait at least 30 seconds, then plug it back in. After about five minutes, which gives the modem time to be fully up and ready, try connecting one or more of your WiFi devices and see if they stay connected. It may not help, but sometimes power cycling the modem can fix certain issues, in the same way that restarting a computer or other device can sometimes do so.
Thank you for contacting us and welcome to the community. I am sorry to hear you have been experiencing this. After running diagnostics, it appears that we do not have communication with your modem. When looking through your diagnostics history, I see very poor alignment when it comes to the dish's position. In light of this, I would like to send out a technician. The technician will be re-pointing the dish and performing other preventative measures to maintain the repair. Please private message me with days and times that would work best for you. Keep in mind scheduling an appointment for a specific day may be difficult depending on the availability of the technician. Because of this, I will review the schedule based on your answers and present you with the ones that match the closest. Also, please include a primary email and the name and phone number of the person most likely to be there for the repair, in your private message to me. This person does not have to be yourself, but they must be over 18 years old.