I have had the same provider NC/NS on me three times this week.
Granted, the first two we did not have a firm date set (according to the "rules" set out elsewhere in this thread), and she did apologize within a few hours, but we most certainly had a firm date set for today. Time, place, attire, etc was all agreed upon in advance.
I was completely expecting another NC/NS, so today wasn't a surprise, but she's on my DNC list now. Things come up. Life gets in the way. I get it. But not three times in a week. Now you're in rudeness territory, and I have better ways to spend my time and money.