Just to add a little .....
You can get a more detailed report for a given time period by adjusting the "sliders" at the bottom of the GlassWire display:
There are a couple of points that you need to keep in mind:
#1: GlassWire will only track and display usage for the single computer that it is installed on.
If you have multiple computers you will have to do a separate install on each machine and add the totals.
#2: Keep in mind that having a router connected makes things more difficult as it allows multiple devices to share a connection and the wireless portion is the worst.
As an example I brought my Samsung Galaxy tab 4 home from work for a few days. Despite it being set up to NOT update some installed apps continued to update. The data used was not recorded by GlassWire because it can't be installed on that device. The tablet consumed about 800 MB of data in the few days it was home.
I would encourage you to remove any router from the network during the troubleshooting phase. Connect a single computer directly to the modem.
Test each computer separately over a few days and see what programs or processes are using data.
Remember also that users running Win10 have very little to no control over what and when Win10 updates or the info it "shares".
Also keep in mind that Microsoft is "preloading" Win10 to users of Win7, 8 and 8.1 as a background process.
If you have any questions regarding the use of GlassWire or general data loss issues just post them to this topic and I'll do my best to assist.