Prepaid Nightmare

I am trying to activate the prepaid SIM card I ordered. I am bringing my own device (it is new) and porting my phone number from my former provider. 

According to the Number Transfer/Port Status page, my port status is confirmed.

According to the AT&T Prepaid Activation Portal, "GA309 : Oops, we hit a snag. Come back later and try again."

Various numbers and webpages which I've frankly forgotten because this is a huge headache and the labyrinthine pages of unclear nature stretch into endless infinity have suggested that the SIM is already activated. 

I have tried the main helpline, as well as 888.898.7685, which supposedly specifically assists with porting numbers. Neither will recognize my cell number (the one marked confirmed) as an AT&T number. It is impossible to speak to a real person.

I cannot make calls from the phone. 

I am loath to go to the AT&T store, particularly because the one nearest me (quelle suprise!) doesn't allow me to make an appointment in advance. Looking forward to clarity on this issue.