In this case it might be easiest to simply make up an excuse, they want to change teachers anyways, so you have just been asked to do some accompanying at that time and unfortunately won't be available for the next 2 months. Period. It's funny though, I always let student's choose music they want to play, when appropriate, and yes they all want to play the theme from twilight, Taylor Swift, One direction, etc, but after a while they will come back at you that you aren't strict enough and don't follow a proper methodology. Therefore you are a 'bad' teacher. So I try to do both, find a balance, but also do keep advertising, keep a full schedule, and keep these kind of students/parents out of your life and mind.