randyill221
A 12.1.9 State Code means a transmission error has occured. This can be caused by a number of things, and a rep will probably run remote diagnostics on your system to determine what may be causing the issue if it is a common occurence. In the meantime, it's best to leave the modem powered so it doesn't lose any of its internal diagnostic codes that can help a rep to determine if there is a problem.
Some of the code definitions can be seen by hovering over them if they pop up in the System Control Center. You can also Google the codes, and may find definitions for certain codes on Google that link back to a thread on this Community. As for an actual list, only techs and Hughesnet themselves have that.
How much data is Hughesnet taking away for you to ask these questions? Posting on here uses VERY LITTLE data as it's mostly text. Maybe 1MB? It's a question I've never seen asked before, so I can only guess at the amount.
Your data usage being high can be caused by a number of things, and you need to drill down what that could be. The following thread contains a lot of information, and much of it will probably be helpful in reducing that usage. https://community.hughesnet.com/t5/Tech-Support/Understanding-data-usage-data-loss-and-connection-paths/m-p/78602#M55972
But, with that said, data usage, and it's reduction, is the user's responsibility. Hugehsnet doesn't replenish peoples' data because of a user's high data usage. This is why it's so very important for the user to figure out what is using the data and adjust things so that it's not being used up so quickly.
Auto program updates. Syncing in Windows. "Updates from more than one place" in Windows 10. Adblockers for browsers (Adblock Plus is the most popular). Turning off auto video playing in Facebook. Using Glasswire to determine what's using the data on a Windows computer (explained in the linked thread). DirecTV receivers can use a ton of data when connected to Hughesnet (usually advised against). Etc.
There are a ton of things that can use data without it being obvious or the user being aware. What's listed above are many of the most common. The linked thread contains a lot that can help.