“I’ve got more important business to do so I’ll cancel this meeting.”
Of course, you’ve got more important business to do. That’s out of the question. The real question is why did you agree to the meeting in the first place?
It’s easy to schedule a meeting when it’s a week or more away. It’s much more difficult to schedule a meeting that you actually want to attend when the day has come.
For me, the following question has proven to be a valuable tool: What would this meeting that I’m about to agree to need to provide so that I absolutely wouldn’t want to miss it? Make this specific before agreeing to the meeting. State it clearly and publicly.
Because if people would be ok to miss the meeting, then why should it be ok for the others to reserve the time just in case? If you feel that it will be ok to miss a meeting, you might just as well skip the meeting and schedule one that you wouldn’t want to miss, instead.