This is a very frustrating problem, and your agitation is understandable.
Hughesnet sells you data; it doesn't use your data. Something on your side is using data, and it's up to you to figure it out; this isn't something the ISP can do. What things do you have connected to your wifi? Do you have smart appliances? Do you have a TV connected to the internet?
Next time when you leave the house, unplug the modem. There will be zero data usage while the modem is unplugged. You can unplug it when you go to sleep too. No electricity to the modem = no data usage. One thing to keep in mind with this is that when you check the data again, you may see data usage: that will be the number from when you turned off the modem, not new data usage.
You can install the free Glasswire software on any Windows or Android devices that you have to see what's using data. But if the data is being used by smart devices (TVs or other), you won't see that on Glasswire, which means this is limited, but may give you some idea. Many things update themselves and that uses data.
Here is more information about testing for data leaks: https://community.hughesnet.com/t5/Tech-Support/Where-s-my-bytes-Testing-for-data-leaks/m-p/77194#M55085
