@rcschnoor easier said than done. After my posts in June, I actually downloaded glasswire app to try to prove what was going on by monitoring data completely and seeing which of my over 200 apps were using data.
It IS easy and I'm not sure the need to use glasswire. ALL smartphones have a built in data monitor which tells you how much cellular data each app uses which is independent of Verizon or any other cellular provider you may be using. You don't need to trust Verizon for counting the data and you don't need to download a 3rd party app. ALL smartphones have a built in app native to the device's OS which will let you know how much data your apps use. Glasswire probably just takes the data already gathered by this native app on your device.
For example, I just checked my current cycle data usage with the first page shown below.
Looking a little closer, I saw something which was a little surprising since I didn't think I was using that much data with the Times Union(local newspaper) app. I rarely look at this app on my phone.
This app has used 250 MB of cellular data even though I don't remember opening it during this billing cycle and 237 MB(background data) of that usage was when I wasn't even using the app. Just ONE example of how your data usage can be higher than you think it is even though "your habits haven't changed". This is an app I rarely use, yet it has used a quarter of a GB in the first week of my billing cycle! I'm sure it is possible that MANY people have similar apps which are using background data on their device which is increasing their total data usage.
Yes, I/you could disable background data on apps, but then people would be complaining that they no longer receive notifications from their apps. The app can't show a notification if it can't receive data in the background. That is the catch-22 in data usage. People want their notifications but don't want to use too much data. It takes data to receive notifications.
Another example of an app on my device which used more data than I had realized(125 MB out of 127 MB was used in the background when not using the app) is shown below: