Why is my HTC One A9 SIM card suddenly not reading?

A

AC Question

My HTC One A9 Wi-Fi suddenly started displaying the following message, whether or not I turn off Wi-Fi

Wi-Fi Calling Error
Error: ER05 - Invalid SIM card

When I tap that notification, the following message comes up:
Important Notice
Your SIM card needs to be updated for Wi-Fi Calling service compatibility. Please visit a T-Mobile store or dial 611 from your phone to reach Customer Care.

I cannot call from my phone; it keeps disconnecting whether I try using Wi-Fi or Mobile Data.
Upon further investigation, I see that, even though my Mobile Data toggle is on, a message shows which says "Disconnected because service is unavailable"

>>> why is service unavailable!?
My account is current. This doesn't make any sense... HALP!!
pls :)
Thank you very much, Erin
 

B. Diddy

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Welcome to Android Central! The SIM might just be faulty. Go to your T-Mobile store and request a new SIM.