How do I stop apps from using mobile data?

In the Android Mobile network settings, tap on Data usage. Next, tap on Network access. Now you see a list of all your installed apps and checkmarks for their access to Mobile data and Wi-Fi. To block an app from accessing the internet, uncheck both boxes next to its name.

How do I tell which apps are using data?

On Android you can get to the menu by going to Settings, followed by Connections and then Data Usage. On the next menu select “Mobile Data Usage” to see a rundown of what apps you’ve used so far this month and how much data they use.