I'm sorry, but just to clarify, is your problem with the
MDE Mobile App? Have you tried accessing MDE on a computer?
If your reservation appears when you log onto MDE on a computer, then it is probably a glitch with the Mobile App. I would uninstall / reinstall the App. Sometimes that helps. If the problem persists, report it to the App Store. The worst case scenario is that you're stuck making reservations on your computer.
If your reservation isn't appearing even when you log onto MDE on a computer, I would be more concerned. Is it possible that Disney cancelled your reservation and refunded your deposit and any payments you made? Is it possible you made your reservation on a different MDE account? The reason I ask is that my mom and I both have MDE accounts from different vacations, so I would be the type of person to forget which account we're using, lol.
Maybe call Support again tomorrow? If it were me, I would kindly bring up the fact that I make reservations directly through Disney to prevent these kinds of problems from happening.
I'm sorry this is happening to you and I hope the problem is resolved soon!