Let's try a few steps to get this working again.
Please switch off your phone > Remove the SIM > Wipe the gold contacts on the SIM with a clean cloth > Reinsert the SIM > Switch phone back on. This tends to fix a lot of issues!
Have you recently ported your number from another network? If so, please get in touch with your network provider as it may be an issue on their side.
Thanks for confirming that for us, @s9user123. Have you got another SIM that you could try in the phone? If another SIM works fine, we would recommend trying a replacement SIM from your Network provider to resolve this.
Have you been in touch with your network provider to check if there's any restrictions on your account? If there's no restrictions on your account, please try the following steps to reset the APN settings:
Settings > Connections > Mobile networks > Access Point Names > Menu > Reset to default.
Once you've reset this, add the APN settings again, or ask your mobile network to send through the correct APN settings:
Settings > Connections > Mobile networks > Access Point Names > Add > Enter the details > 3 dots in the top right > Save.
*Please note: if an error pops up saying "APN settings are not available for this user", ignore this message and continue with the set up.