I don't personally have Apple TV, but after doing a little bit of research it may be possible that the Apple TV is still using data. If you don't already do so, it may be a good idea to unplug it when you're not using it to ensure that no data is being used by it. Updating wallpaper is one of the things mentioned that keeps using data in those devices.
I'm also seeing posts from people who are claiming that Discord is using a lot of their data, though only while they're using it, of course.
Unfortunately, it's probably going to come down to a process of elimination in order to determine what it is that is using so much data. I'm assuming that you're using the built in WiFi of the HT2000W, and that doesn't break down usage by device, so what you're probably going to have to do is refrain from doing one of the activities, like Discord, for a day, and see if the data usage has drastically dropped. You can also disconnect a non essential device for a day, or at least a while, to see if the high data usage disappears. Again, it's going to be doing it one by one. 5GB per day is a HUGE amount of data if you're not streaming, so you should see the data use drop when you hit the right program/device that is causing the high usage.
Just in case, this page can tell you what devices are currently connected to the HughesNet modem, and what devices have been connected, and subsequently disconnected, since the last time the modem was powered up. I mention this because sometimes there can be devices connected, and possibly using data, that a person may not be aware of or may have simply forgotten about.
Also, as mentioned in the other thread, if you have a satellite TV receiver connected, it's best to disconnect it, as they can use a large amount of data, even when they are not actively being used for on demand. The data they can use usually varies greatly and tends to hit all at once when it does, though.
The following two posts also have a lot of useful information that can help with this type of issue. Something is most definitely using a lot of your data, and what that is needs to be figured out and stopped so you don't have to keep dealing with it. And, like mentioned, it's almost assuredly going to come down to process of elimination, with the only other real option being spending a couple hundred on a 3rd party router that can monitor data usage by device. I doubt you want to do that. I know I wouldn't.