A parent is spreading malicious lies about me on the internet because I kicked their son out of my martial arts school.

I took the child out of my martial arts school for his aggressive social behavior against other students as well as his sexual innuendos and rudeness in my class as well as profanity. His destructive actions have caused a lot of stress in my school so I have asked his parents to take him out of my school and they are now spreading malicious lies about myself and other students in the school as well as calling my students illegal immigrants and that they will turn them over to the law enforcement. I never did anything except try to treat their son with dignity. I just want them to stop harassing me on the internet and spreading malicious lies and rumors about myself and other members of my martial arts school. It is definitely a factor and may harm my business.