Great. That rules out your devices microphone then. However, I recommend you to run the microphone diagnostic in your Samsung members app, just to be sure.
To rule out any 3rd party apps or customisations that might be causing your issues, please boot to Safe Mode.
To get to Safe Mode - Long press Power button, long press Power off icon, tap Safe mode icon. (When booted into Safe mode, you may need to turn off flight mode as it sometimes enables itself) Take a call and see if your issue has gone. If so, then you know it's one of your 3rd party apps or customisations that were the culprit. It's then up to you to determine which one by a process of elimination.
If that doesn't help, try turning off wifi calling if you have it.
Finally, try a hard reset
With the phone powered up, hold Volume down button and Power button simultaneously for 10 seconds. The screen will go off. Continue to hold buttons until the phone vibrates and the Samsung logo appears. Release buttons. The phone will reboot. Once done, please check if the issue is resolved.
If still not resolved then reach out to your network provider and ask them to check for any issues at their end.