Trouble Using Phone after activating sim card

I was looking to transition from Mint Mobile back to AT&T and I recently purchased an AT&T prepaid SIM card online. I chose to retain my current number when I made the purchase

After receiving the sim card, I turned my phone off, put the sim card in my phone and powered it up.  I attempted to activate the sim card but keep receiving a GA309 error.  

I've attempted to restart my web browser, clear my cache, restart my computer without any luck getting past the GA309 error.  So I went to an AT&T store for help.  They were unable to help me because I purchase the sim card online but an AT&T corporate location would be able to help.  So I went over there only to be told I need to call the help line for assistance (which I can only do by changing out sim cards for the Mint Mobile plan).  I call the AT&T prepaid customer care number and try to use the automated activation but they can't find my phone number and when I try to activate the sim card the automated line says the sim is already activated.  I can't get ahold of any human's to help with this issue.