ATT Cannot cannot 'Port' Legacy POTS Number to ATT Digital Voice

This is a frustrating issue that I wish somebody could shed some light on.  I have an existing telephone number in NPA/NXX 248-599 and I'd like to change it to an old ATT POTS line TN that I used to have in the NPA/NXX 248/377.  The ATT rep yesterday of course said 'no problem I'll get that order in and it will complete at Midnight'.  Well that didn't pan out and when I called support today I was on the phone for almost two hours and eventually the rep said there was an error placing the order and ultimately the number could not be 'ported' because it was an inactive ATT legacy POTS line.  That makes no sense at all to me.  First of all why would it be considered a 'port' in the first place?  Is it because my incumbent OCN is 516C whereas the desired NPA/NXX OCN is '9323' - Anyway wish I could the desired number but it looks like nobody at Ma Bell can make it happen.