Not practised in Poland.
I always practised that ... and it worked ... but then again, I was adored by all my students (especially the teenage boys ; ) ....
Poles aren't exactly unreliable, but what they are is pretty ruthless, and they will usually do what is right for them, without any scruples.
You might get the odd lesson missed, but usually only due to genuine reasons, and usually made up and accompanied by a lot of apology.
If you are getting a lot of cancellation/not paying, I'm afraid to say that is because they probably aren't happy with the lessons. They won't be English and say 'sorry, this just isn't working out' - they will just vote with their feet.
Sorry to say that, but my advice is: think about how you are as a teacher, and how good your lessons are, and how satisfied your clients are. Students who enjoy the lessons and feel they are worth it will not cancel, and will pay.