[ZombieBerry]

I don't think your provider would be able to help.

Open Calendar and swipe from the bezel and select 'Manage Calendars' Are you using multiple calendars? Do you sync them with your computer or online service (Yahoo, MSN, etc?)

You can also check under Accounts (under Settings>Acounts)

Are these disappearing appointments ones that you have made or are they invites from contacts on your device?