You don't get to say no to assignments, if you do they won't pay you for that day, and if you refuse too many you get in trouble/potentially fired. They will trust anything a school says about you more than they trust what you say. They're in it to keep their contracts with schools, not stand up for you individually. Getting in contact with my assigned consultant/supervisor was very difficult, and I often had to reach out to other people in the organization to get help or questions answered.