Keep in mind that Mama Melrose also gets mixed reviews. (As does Hollywood and Vine).
Call again and ask about availability at Mama Melrose for the night you want, but it is probable that there is simply no availability for the night you want at the time you want. This is very likely because you were able to get reservations at the other two restaurants.
But considering that Fantasmic is only performed twice a week during October (unless they change the schedule the week before you arrive and add an extra night) I think I’d hold onto whatever dining package you can get. Either that, or eat after Fantasmic. The odds are very good that the amphitheater will be standing room only and the show is about 27 minutes long.
I’ve got the same problem with Fantasmic only being performed once while we’re there, but it’s compounded by having tickets for the Halloween party the same night!
(But I can watch my video anytime, so it’s not quite such a big loss for me)