IPhone 12 Pro not getting calls

I have had my new iPhone 12 Pro for three weeks. My wife had told me that every time she calls me it went straight to voice mail so I went back to t-mobile/sprint and they replaced the T-Mobile SIM card with a Sprint SIM card. After a few days my wife told me the same thing kept happening every time she called me so I got on t-mobile chat with their support team. They walked over a bunch of things with me and reset my network connection and a lot of other stuff that took well over an hour. Realized this morning I am still having the same issue! Is this a Phone problem or a network problem and if so what can I do to resolve it - I rely on this phone for work!