[SOLVED for Me. Might work for others]
I had something like this issue on my Note 9. The issue being I could never hear incoming calls and the caller couldn't hear me. Turns out it was WIFI calling that was causing my issue. At first I thought it was voicemail but it is Wifi calling. I am based in the U.S. so this might not apply to EU people but just in case, disable wifi calling and see. I think there is some issue with my ROM and my carrier which isn't a major carrier that supports Samsung Note 9
See if turning off Wifi calling helps
You are still having the issue?
Okay so last night I got my other half to call me as per usual he couldn't hear me . While his phone was still connected I started to do all sorts. I put WiFi on and off put data on and off loud speaker on and off I did Bluetooth on and off . I finally pressed hold on and then off . Guess what it worked . I've called of myhome landline and work line and I still have to put the call on hold and then take them off hold In order for them to hear me. But that's better than me missing call.
I'm going to deal with it like this till the next update to see if the next one resolves the issue .
Good luck all
+1 for me with Note9. Since Jan update my colleagues were becoming incredibly frustrated let alone me. I notice there is about 5 or 6 threads all the same topic since the turnover of the year. This is a wide spread problem they need to fix. Sick of calling people back. This is just not on - very clearly the software issue that started early Jan - Fix it Samsung!!!!!
My s9+ has been having the issue for ages. Turning off the WiFi calling seems to have worked for me. I am in the UK with a major service provider. I cant believe Samsung have still not sorted this out. Thanks for the fix