I like to calmly inform them that I will not be paying them ever. This usually results in them telling me that I have too. Then I explain that I am infact an adult and I don't have to do what they tell me to do. They usually get angrey now, at that point I explain that there's no real reason to get upset somtimes you lose some and they probably should not bother to call because I will be blocking there number if they call again. They usually hang up at that point.