Is my Android asian phone blacklisted?

My Xperia 1 III had been working fine since I ported from AT&T to T-Mobile in Feb 2024. Although only one 5G band is available, I've never had any issues with VoLTE or VoNR not working. 4 days ago, on June 7, the phone stopped connecting to the network. I spent hours on the phone with support and another two hours in the store. A new sim did not work either. I've had to use my old Pixel phone as a replacement for now. When I open the diagnostic screen, I watch the phone bounce to every available technology it can find (GSM, LTE, etc.) but it fails to connect. T-Mobile must have pushed a change on their network a few days ago. I am still waiting to hear back on the status of my trouble ticket.