As a process if elimination can you try your sim card in another phone.
Also try done troubleshooting tips such as …
Current Phone > Samsung Z Fold³ 5G.
@1gill: Are you currently inside the region where you activated your SIM? Can you try opening the Phone app > Tap the 3 dots in the top right > Settings > Supplementary Services > Call Barring, and make sure the options here are toggled off, especially 'All Incoming Calls' and 'All Outgoing Calls'? Also, head to Settings > Connections > Flight Mode, and make sure that this feature is disabled.