APN = Access Point Names
Find the APN settings of your provider
Now you can check the APN settings on your phone
1 Go to the app Settings
2 Choose Network & Internet
3 Tap on the name of your SIM provider
4 Scroll down and there you see Access Point Name
5 Tap on the name and check the settings.
When the settings are wrong, tap on the name and alter the settings.
Save your changed settings by tapping on the 3 dots (right upper corner of the screen).
If no name is shown there:
Click on the + (right upper corner of the screen)
Type the APN details of your provider
Then tap on the 3 dots (right upper corner of the screen) and tap on Save.
After point 4 there is also the option to set the APN to default by tapping on the 3 dots (right upper corner of the screen) and choose Reset to default.