OP, please write in. I wouldn't call, I wouldn't wait til you check in, I would absolutely call in.
You are spending, likely, thousands of dollars on this trip. You probably made your dining choices at 6 months and your fast passes first thing in the morning at 60 days. You've played by Disney's rules and they've changed the game with just over a month before your trip. That is not right. You shouldn't have to bend over backwards and rework your entire trip because they were seduced by extra money. They could have very easily said, "I'm sorry, we require notice of 61 days for this type of rental as it disrupts the general operation of the park and our guests who have already scheduled their dining and fast pass plans." But they didn't. They took the money and shoved you out, essentially.
As you said, the parties are advertised in advanced. This is just absolute nonsense. And it is as unacceptable as when they closed CRT and cancelled guests' reservations for a "chef's table" event.