Is it a property perhaps that Hilton manages but doesn't own?
I had refund problems with a reservation in Cancun that I had switched from a one night deposit transaction to an AP for the whole 10 days. I couldn't get the deposit refunded on a timely basis and Hilton kept saying they had contacted the hotel to refund it and kept acting like a third party. I finally called the hotel accounting dept. directly and they confirmed that Hilton sends them deposit and AP money nearly immediately upon receiving it at the time of the reservation.
Hilton is not very up-front about hotels it doesn't own but has management contracts to run (like Cancun).
I have no idea if this has anything to do with the slow response you're getting after not receiving credit for your AP -- but thought I'd mention it.