How do I remove AT&T NumberSync for Connected Car

I was setting up my new Apple Watch which seemed to work fine, but afterward I received an email that said "AT&T NumberSync for Connected Car Confirmation".  I didn't intend to change anything for my car and don't know how this happened.  Now my car isn't responding normally.  It no longer knows how to send a message (normally I would just be able to say "Send a message to xx", but it now doesn't recognize that and only wants to make a phone call).  In addition, when I say "Hey, Siri", Siri comes up on my phone as if she is listening, but she doesn't respond when I talk to her.  Since I don't know how I made this change, I don't know how to undo it and I haven't been able to find any applicable information.