You've activated manual network selection and are out of range of the selected network
Possible cause 5 of 9:
If you're trying to access the Internet using the mobile network and you've activated manual network selection, you need to be within range of the selected network.
What you need to do:
You can set your mobile phone to select a network automatically or you can select a network manually. If you select a network manually, your mobile phone will lose connection to the network when the selected network is out of range.
Find " Network operators"
Slide your finger down the display starting from the top edge of your mobile phone.
Press the settings icon.
Press Mobile data.
Press Network operators.
Select one of the following options:
Select a network manually, go to 2a.
Select a network automatically, go to 2b.
2a - Select a network manually
Press Search networks.
Press the required network.
Your display will tell you if you have access to the network you've selected.
2b - Select a network automatically
Press Select automatically.
Return to the Home screen
Press the home icon to end the session and return to the Home screen.