Hmm that's extremely odd that it happened out of the blue, priyapam. If you're disconnected from WiFi, do calls go through or are you only having issues with texts? It sounds like iMessages are working probably and maybe WiFi calling is working for you too. Do you happen to have a different T-Mobile phone to test your SIM in?
Good morning, priyapam!
I just wanted to swing by to see how things are going with your phone today. Are you still receiving errors related to the iPhone not being activated or is everything good to go now?