New vehicle device

Anyone know why AT&T (Edited per community guidelines) so bad at enrolling a vehicle to an existing phone plan account?  I've been on the phone for an hour and I'm on my 3rd rep who is trying to figure it out.  I swear, you'd think I was the first person ever in history to want to do this.
Yes, I know there's a website for this, but it doesn't work either.  It said "call this number so that our clueless phone reps can fail to help you"