2.
Turn Use Data Saver on  .
You'll see   in your status bar and all apps are prevented from using background data.
 
Tip: The first time you turn Data Saver on,   is added to quick settings. After that, just swipe the 
status bar down and tap   to turn Data Saver off/on.
3. To allow certain apps to continue using background data, tap Unrestricted data, then next to the app 
name, slide the switch on  .
Restrict for specific apps indefinitely
1. Go to Settings > Network & internet > Mobile network.
Or, in quick settings, touch & hold  .
2. If you're using two SIMs, tap the SIM name.
3. Tap App data usage.
4.
Tap an app, then turn Background data off  .
Dual SIMs
If your phone has two SIMs, cellular data is active on only one SIM at a time. You can control which SIM is 
used.
Settings : Network and internet 156