Unable to send text to contact

I have tried everything.  Went into a TMobile store.  Associate was not interested in helping me, then when I asked again, he called customer service and just handed me my phone to trouble shoot.  The person on the line told me a to do a few things, then told me to restart my phone.  I was able to send a text to my contact one time.  After that, my phone went back to not being able to send to the one contact again.  I checked block sender settings and they are not blocked.  No one else has been blocked.