Cancellation Courtesy

On Wednesday nights, I teach piano to a very select few children (3-the families go to our church and are in choir with me). I have a few rules for my lessons:
1. Lessons start on the 1/2 hour or hour, so don't be late!
2. Parents cannot stay for the lesson. They can stay in their car or go & run errands and come back when the lesson is over with.
3. If you cannot make a lesson, call at least a day in advance. If the call is made the day of the lesson, you will still be charged (exception: illness).

Sounds easy enough, right? Wrong! I have one family that breaks two of these three rules quite consistently. And it drives me absolutely nuts!!! They are 5-10 minutes late every week and twice in the past month and a half have called to cancel their lesson. That would be fine, but they are calling 30-60 minutes beforehand. How incredibly rude! It just frustrates me because I had planned on calling them on Sunday and canceling this week's lesson so that all 7 of us (mom, dad, me, Mark, Ethan, Travis and Jenna) could go out to dinner for Mom's birthday. But I being of extreme sense and courtesy decided that wouldn't be very polite. Well, screw politeness! Next time, I'm doing it! And I'm keeping my 8 whole dollars!!! GRRRRRR!