OP: I'm glad you got the situation sorted, although it's an unnecessarily convoluted process. They should've just let you renew your AP.
But, well, I'm just chiming in to say that I hope all goes smoothly when you renew your AP and want to use the ticket you bought (or are going to buy) to pay for part of it because you might run into another ill-informed CM.
I had something a bit similar to this happen to me several years ago. I had a ticket that I converted to an AP (oh, those were the days!) and I realized when I got back to the room that they'd overcharged me. I consulted with Robo here, got all my facts and figures straight, and went to Guest Services at a different park . . . where I was told that the CMs are always correct, there wasn't a mistake and they owed me nothing. These statements were delivered to me in a very un-Disney-like tone.
But . . . they were wrong. After I got home, I called the ticketing number (I don't want to give it here in case it's changed--but check on the thread that's all about tickets, where they know the score) and indeed I was correct and they credited me the money. It wasn't even all that much--less than $50, iirc--but I was just pissed that I'd been overcharged and then insulted afterward. So I was determined to get my money back.
Anyway, I hope this doesn't happen to you, but be prepared with all the info you need before you call to have your 1-day ticket converted to help pay for your AP renewal.
And enjoy your trip! I was so relieved when I got to your post where you said the discount you wanted was still available.