How to check if my Android device supports the carrier's VoLTE?

Straight Talk, my carrier, informed me that my phone Xiaomi Mi 9T pro is not capable of using VoLTE. My phone states it is enabled for VoLTE. Also has an icon (volte) next to my status bar. I was also told I could lose my service end of Feb. 2022 if I did not get one of their phones. At this stage I don't know what to believe. Any answers?