I don't really know much about AARP/CHASE etc however here is an older thread which may help? (It seems calling back and speaking to a different agent has been the case before to make it successful but some mixed results and reading between the lines officially, historically speaking, it seems it isn't allowed but happy to be corrected if there's been any changes)
I assume there was availability to upgrade in the first place?
I think my fellow former Ambassador
golfmad has some working knowledge on your query and hopefully he can provide more of an insight with his experience in such matters.
Can't Upgrade AARP Club World ticket to First?
ETA: See here too
https://www.flyertalk.com/forum/27543939-post16.html
Pete