Did you book with the drink package promotion that was running recently? It did end recently (like end of August), and it's definitely one that if you change or refare or whatever they don't let you keep once the promotion ends (which is true in general of all the promotions they offer, I'd expect most cruise lines would be the same way). I'm kinda surprised they told you that you could keep it if you changed after it ended, so yeah, I'd say that's incompetence on the part of whoever you were talking with. (I've been debating whether to refare my december cruise because the price is lower, but I'd lose the drink package, the amount of the difference in fare is borderline on whether it's worth it.)
I never book directly with the line myself, I've always dealt with a TA I've been using since I started cruising.