The utter and abject failure of my encounter with T- Mobile support of the Cellular option provided by Apple Watches.

@JimOS 
I would appreciate hearing of the resolution to your issue. I've just been through a 2-day nightmare with TMobile. I have had conflicting information about their "cellular" service and what it does and does not do. I know it worked with my old Apple Watch with the same cellular plan but for some reason with the new SE Watch it no longer works. I won't bore you with all the frustrating details, but for 3 TMobile tech agents not to know that others have had this same issue is a breakdown of communication within TMobile. I finally deleted my "cellular" plan from TMobile and now relying solely on the Wi-Fi for my Apple Watch connection. Crossing my fingers that will work well enough but not what I wanted the watch for in the first place. I have been with Sprint over 20 years and now with TMobile. I never had this kind of problem with Sprint. Sad.