I have Samsung S21 on 2 degrees network

The outbound and inbound calls were not working. Messages and data were working. It was probably like this for a few weeks as I email. txt and WhatsApp mostly.

Settings on the Samsung showed 2 degrees as the carrier but with an unknown number.

I tried a number of solutions- turn on and off phone, removed SIM 1 and cleaned, turn on and off flight mode.

They did not work

The phone was set to 5G preferred. It had been like that for a while

I then turned on the VOLTE calls SIM 1 

"Use 4G data networks for calls where possible" to ON . It had been OFF

The SIM manager now shows the correct phone number rather than "unknown" and calls can be made and received.

I would appreciate advice as to whether this may be a 2 degrees problem or a Samsung problem as I thought 5G would be used.