Try a soft reboot by turning the phone Off and On @geo2020
This could be mast issues or issues with your sim card or the phone.
If you can check your Network Masts via any available Status Checkers.
Have a word with your Network Customer services to ensure it's not your account.
Sometimes a sim card fails to which a Network can perform a Sim Swap to replace it.
Is this happening everywhere and with all incoming calls ?
If certain callers then both check you've not inadvertently added each others numbers to the call blocking feature.
Try going into your phone's connection settings and choose another network and then re choose your network. This helps to refresh the network connection.
Can you make outgoing calls ?
As a process of elimination can you try your sim card in another phone and another sim card in your phone ?
🌈 Stay Safe & Stay Alert. 🌈
Daily Driver > Samsung Galaxy s²⁴ Ultra 512Gb ~ Titanium Black.The advice I offer is my own and does not represent Samsung’s position. I'm here to help. " This is the way. "