Swipe to accept the call, call timer remains on 00:00, call is dead already.

I have been ATT customer at the same address for 15+ years. Last month changed to T-Mobile with brand new iphone 15 pro and having many technical issues. once a day its either a call drop, not able to hear other party or call not going through at all. Recently, a new technical issue popped up. When receiving call, I swipe to accept. I can not hear other side, so when I check screen, the call timer remains on 00:00!! The person left a VM and that arrived NEXT Day full 24hr later. It was a highly important call and I am SO FRUSTRADED. No one died, otherwise instead of this forum, I would be on legal law firm forum, and thinking about service millineries use!?