Below is an email I just sent. Should you find that your time is not respected and you are being taken for a ride in your job search, feel free to reference this. Don't burn bridges, but definitely advocate to be respected.
Good morning,
Twice this week, we had a scheduled call that did not happen at the time it was scheduled. My time is important, and I told you that Friday was already tough and booked for me. As such, please remove me from this candidate pool. Thank you, and good luck in your search.