Update: this issue is resolved. I didn't get any notice from anyone (the ticket was still on hold), but I dialed my home number and it rang.

I did have to raise this issue to a higher level before someone in support would do more than just "sorry they took it. We submitted your port request but that got rejected without an account number that we know you don't have, but we can't do anything about it and you can contact AT&T yourself." Better training and more perseverance on the part of the support staff would help. I understand it's not Voipo's doing, but dumping it back on my lap to contact AT&T myself was definitely not the right move. In the end, I'm glad I got my number back.