I've had a similar issue in the past. The teacher would frequently cancel last-minute. Of course, since the class didn't take place, one can't leave a review.
However, if you, the student, immediately report a lesson problem instead of confirming the lesson, you can state that the teacher didn't attend and didn't give notice, and that therefore you want a credit refund, not rescheduling. I'm curious why you didn't use this option after it happened more than once. That way, the teacher can't first report that there was an "agreement" and make you reschedule the lesson. It won't show up as a review, but their attendance rate statistics will reflect the missed lessons, which, in my opinion, is fair if this happens more than once.
italki won't block the teacher or stop them from teaching right away. However, there are various steps the teacher would have to take to explain what happened to support and it would serve as a warning not to make a habit of it.