Hi, Janine! Don't give up! The best thing you can do is keep on calling. While cancellations do happen, there is not a waiting list so you just have to time it right.
Try a few things. First, and this one isn't fun, log onto
www.disneyworld.com at 6:00 a.m. EST. and try to book your Advance Dining Reservations online. Reservations cancelled from the prior day will be released by this time and hopefully you can get that special dining experience! If the 6:00 a.m. is too early, the phone lines at (407)WDW-DINE open at 7:00 a.m. EST. Give this a try, too!
Another online tip: when booking online, don't just check for the day, click for a "date range" to include all your vacation dates. You never know what surprise might pop up!
If still nothing, check with your resort concierge, or even try walking up - you just never know! Make sure to be flexible, ask for early dining or a late seating. I know when it comes to dining with Mickey and his pals, we parents will do anything to get that reservation! Good luck to you!