Both sides are required to be at a hearing. Period.
If a specific date and time don't work, the lawyer is supposed to ask for a continuance. If it is granted, a new date is given. If it is not granted, the lawyer (or a fill-in) is required to be there. If a true emergency exists, such as the person was in an auto accident on the way to court, then that's different.
From what you've said, it sounds like there was a screwup. Might have been your lawyer. Might have been the court. Courts have been known to give the wrong dates.
Lack of preparation is NOT a valid reason not to show. It might be a valid reason for a request for a continuance, however.
Hope this helps....