I recently ported my phone number to Verizon but switched my number back to AT&T because of the incompatibility of a Verizon sim with an old AT&T bought iPhone. This happened in a span of two days, July 10 (When I switched to Verizon) and July 11 (when I switched back to AT&T for gophone). I could send and receive texts from nearly everyone except one person.
However, on July 11th, when I switched back to AT&T, I could send and receive texts from this person but the day after, I couldn't receive her texts. She and I are classmates and we've sat down and ruled out the possibility of accidentally blocking each other. We've deleted text conversations and deleted each other as contacts and readded each other as contacts, reset network settings, power cycled phones, called our carriers, and I even went into an AT&T store and an Apple store, but it could not be fixed. I can receive her calls but not her texts and she can receive my texts and calls.
I've done research and it seems like inter-carrier texting between Verizon and AT&T is a small issue and that others have had problems similar to mine, but no recent solutions have been posted.
If one can help my issue, that would be great.