I have been having an issue recently w/my Galaxy S10 where I will be on a call and it will suddenly drop. Then for a period of time up to 20-30 minutes I can't complete an outgoing call (I call out, but it never connects or just drops immediately) or receive an incoming call (goes straight to my VM w/o ringing).
Text & data continue to work during this time, just no ability for phone calls. I will have full signal & I try restarting the phone multiple times but nothing seems to "fix" it until eventually I am able to call again. It used to happen once in awhile, but lately happens almost daily and for longer periods of time where I cannot use the phone for calling.
We understand how important your calls are for you. We know this is frustrating for you. You mentioned that this has happened for some time, but has gotten worse. Have you made any changes to your device or installed anything? Is your software up to date?