You need to tap Continue and sign in to view your billing information.
Verify your payment information or add a new payment method.
To verify your payment information:
Sign in to your Apple ID account page and edit / update your Apple ID details.
https://appleid.apple.com
On the Sidebar click Payment methods -> then tap Payments Methods and tap Manage payment method.
Additional:
Try to do a force restart -> Force restart iPhone – Apple Support (UK)
If it doesn't help, see these Apple articles below:
If you see No Service, Searching, or SOS on your iPhone or iPad
If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support
Manually update your carrier settings on your iPhone or iPad
Manually update your carrier settings on your iPhone or iPad - Apple Support
Update your network provider settings manually on your iPhone or iPad
Update your network provider settings manually on your iPhone or iPad – Apple Support (UK)