Why can I no longer text one of my contacts?

[AC Question]

I was exchanging texts with my mother one day and the next, all my texts failed to go through and still are. A circle spins then an exclamation point pops up in a circle. I can still receive her texts but cannot reply.

 

[B. Diddy]

Welcome to Android Central! You can still send texts to everyone else? Call your mother and ask her if she might have accidentally blocked texts from you.