iPhone 12 not ringing with incoming calls/FT Calls

Hello,

I have a regular iPhone 12, 256GB, iOS 15.2.1 up to date, all apps up to date, on StraightTalk network, over Verizon towers where I am missing regular Calls, FaceTime Calls, and some Text & iMessage messages. This is not for all calls/messages, but occurs with about half of them. Ring Volume also seems to be affected when I use the side buttons to adjust the volume for sounds within apps, even though I have that feature OFF in Settings. I think it has done this since I got the phone brand new from Apple in Nov 2021. Occurs both when my phone is setting asleep and when I have it in my hand & using it. It just will not ring, but sometimes does when it’s setting asleep.

I have checked all my Settings that were suggested in other forum questions and all are set correctly to not do this. Have included screenshots of those Settings I double checked below - Attention Aware is OFF; FaceTime, Phone, & Message alerts are all ON; Volume is set to NOT be affected by Side Buttons, but that seems to be happening when I adjust for other app volumes; physical, side Mute button is OFF!

I really can’t figure this out.