Some devices have Android System Webview disabled.
Devices like this use Chrome instead, to do the same thing.
To enable Android System Webview, Chrome must be disabled, or sometimes the webview can be changed within the developer settings.
Some devices allow this, some do not.
Onwards to something else.
I can't say for sure, but it seems as though he may have another device, and the one you went through is a possible clone of yours.
The idea that the device says 'unknown' for the phone number is odd.
The only devices that I have seen that on are ones that I only use on Wi-Fi.
These are not on any cellular network, and so do not have any phone numbers.
When you have access to his device again, turn off the Wi-Fi on it, call it and see if it rings.
Notice what number comes up on the caller ID. Is it correct?
If he is pretty sly, he could have his mobile number forward calls to it.
Are you positive that his device is a totally different model of phone as yours, yet the model number is the same as yours?
This is incredibly odd, if it is so.
Another oddity is the fact that all of the apps are the same as well.
All of them?
Games and other crap like that?
As I am no expert in things like this, I am asking questions to verify what you have stated.
I try to keep things in life as simple as possible.
At this point, I might consider just getting another device, and setting a lock on it to keep him out.
If you want to continue playing the game, then I would do a few things to my own device.
This could be fun, just to see what happens.
(Yes, I am known to be entertained in unconventional ways, lol.)
First, I would install a firewall onto my device.
This will allow you to control what apps can link to the internet, and if they can use Wi-Fi, mobile data, or both.
There are many available, but there are a few that I have experience with and so will be recommending those.
There are three that I like, and they are at three levels of expertise, or difficulty, if you will.
All do the basic function of limiting internet access.
Easy:
NoRoot Firewall
https://noroot-firewall.en.uptodown.com/android
Medium:
NetGuard
https://f-droid.org/en/packages/eu.faircode.netguard/
Hard:
Tracker Control
https://f-droid.org/en/packages/net.kollnig.missioncontrol.fdroid/
Personally, I use NoRoot Firewall most often.
It is so simple, and uses very little battery.
It is a great way to enter the firewall world, so I would advise to try it first.
Many apps on an Android device are interconnected- meaning that they need one another to work.
This means that you can make part or all of your device (temporarily) non-functional by blocking cellular or Wi-Fi access to certain apps, because they can be part of a slew of other apps.
To compound this issue, it is difficult to figure out what apps are connected to others.
NoRoot Firewall does this for you, by grouping interconnected apps together.
NetGuard does this is in a different way, generally by unrestricting apps that are required for other apps to work, but not letting you know directly.
Tracker Control does not let you know at all.
Start with NoRoot, and block apps that do not need internet or mobile access.
Also, go to
Settings
Apps
(show all)
(show system)
and scroll all the way to the bottom of the list.
Check for any app that has no name or no icon, but is still there taking up space.
All legitimate apps have some sort of icon.
If you find one that does not, you can bet that it is malware of some sort.
The lack of a name or icon will make the app not appear in your app drawer, or other apps that can give you a list of apps on your phone.
If there is such a thing there, then select it, and then tap
Storage
Clear cache
Clear data
(back out to the app's page)
Uninstall
