Just because no one is actively using the internet (web browsing, checking email, etc) that doesn't mean some device on your home network isn't using data. Computers use data all the time now, and when I say computers I mean tablets, phones, and a host of internet appliances like DVD players, DVRs and even smart thermostats. Updates, background data transfers, etc. A few months ago I got a new Amazon Fire tablet and discovered that it was automatically downloading Amazon TV shows in the background - a default setting that I had to research to figure out how to turn it off.
A couple of months ago I noticed we'd been using a lot of data for the month. When we got down to the last day of the monthly cycle we were almost out of bandwidth - to the point where I could see the numbers counting down on the Control Center in my browser. So I started a simple diagnostic: turning things off until it stopped. It turned out to be my iPad Mini. Apparently something to do with a pending update because after I installed the update it stopped eating data.
The same thing happened a couple of years ago. That time it was my husband's Linux desktop computer. Some background service was eating all our data.
So here's a simple diagnostic you can do to figure out where your data is going:
First unplug the network cable from the satellite modem, then wait a while and plug one computer back in - a laptop or something. If the numbers haven't gone down while you're unplugged that tells you it's not a flaw in the modem. Then turn on your internet devices one by one. When the data allowance starts to drop you know that one of the active devices is using data. Start turning them off until it stops.
Do you have a wireless router in your system? It could be that a near enough neighbor is hijacking your data.
