Did anyone mention taking it to the dealer for Android Auto update? lol j/k.
I had to, even though my car was built in April and Android Auto was released in March.
Oh, and try using the factory USB cable that came with the phone. I've heard that helped a lot of peeps.
Some say that you have to turn on USB debugging mode and change the USB setting to MTP mode each time before you plug it in.. because S7 is funky that way with AA.