Hi! At the s9 series release date, I bought a locked T-mobile s9+ & my husband purchased a locked Tmobile s9. His phone never had any problems.
From day one, my phone had horrible call quality. I experienced sound like I was in a tunnel, calls going in & out, static. It wasn't just me. Some members on XDA were keeping lists of what country people were in, along with which carrier & firmware. Antenna issues, they surmised. As updates were released, there were improvements. My call quality became better but not great. This was over a nine month period.
During this time, I realized I had a simular problem to what you described. People would call, I couldn't hear them. But they could hear me running around yelling 'Can you hear me now?' I'd call back, we could hear each other. So embarrassing for me, so annoying to them.
I tried resetting the network, switching sims, wiping the cache partiton, cleaning the ports, toggling wifi & wifi calling on & off. However, I can't honestly remember if I did a factory reset.
I should have returned the phone the first week I owned it, but after fighting with it for 2 1/2 years, I finally bought the Note 20U in August.
I know the above story doesn't help. I think it's hardware related, but again, I can't remember if I initiated a factory reset. It`s worth a try. I really hope you find a solution. Outside of the call issues, I thought the s9+ was a great device.
04-24-2021 04:24 PM