I don't even have a button! Nothing, nada. And the BT connection on my iPhone doesn't show the "show notifications" option either. I drove an Evoque loaner with ICTP while my car was being serviced last time and it worked ok with that car. So, I know it's not my phone.
So, I stand corrected - looks like I'm in the same boat. I'm not sure if it was a recent iOS update, but something wiped out the text capabilities. Oddly enough, when looking at the bluetooth settings, there's the generic "Hands Free" item, and that one DOES have the "show notifications" option - hence my iOS bug thoughts. I may be wrong of course.
I'll check it out in the morning with my wife's phone, I think she's 1 update behind me.