I just called in again earlier and spoke to the Mileage Plan Department and it was as unhelpful as always. A few interesting notes during the conversation,

• After I politely explained what had happened to me, I proactively told her, "I also have the confirmation number if you want to take a look at the reservation." To that, she responded, "Even if you give me the confirmation number, I won't be able to see what went wrong with that reservation."
• She told me there was nothing she could do, but she could transfer me to the reservation line to see if they could help me book a new flight—which I already knew had no availability.
• I mentioned that I hadn’t received a refund for the Partner Award Booking fee, and that didn’t quite make sense to me since I hadn’t chosen to cancel the flight. She said, "Well, when you change your flight, you cancel the original flight and get rebooked into a new one. Therefore, the cancellation fee is non-refundable." And I replied, "But I was never rebooked onto a new flight." Instead of simply asking for my confirmation number—which I tried to offer her at the beginning—she said, "Well, I can't take a look at that if you never give me your confirmation number."

I probably should've at least try to get the $12.50 booking fee back, but ​​​​​at that point, I was just done with speaking to them so I said goodbye and hung up the phone.