To troubleshoot the issue please open the Phone app > Tap the 3 dots in the top right > Settings > Supplementary Services > Call Barring > Voice Call, and make sure that all options here are toggled off, especially 'All Incoming Calls' and 'All Outgoing Calls'. Tap the back button > Call Forwarding > Voice Call, and make sure that all the options here are toggled off. Now, head to Settings > Connections > Flight Mode, and toggle this off if it is enabled.
If the issue persists, please remove your SIM, give the gold contacts a rub, and put it back to see if this helps. If the issue is only affecting certain contacts, please open the Contacts app, select an affected contact, tap the 3 dots in the top right, and select Unblock Contact, if applicable. I also recommend reaching out to your network provider to see if there are any restrictions on your account, or to the service in your current area.
