I don't know who sent a text message to my dad's mobile phone, know my parents and my name, and know where I go to school. I want to give him 20 thousand dollars to threaten me

Contact your parents on other phones in time, tell them the real situation and tell them that this is a scam. Don't panic if you encounter similar problems in the future. Call first to confirm. If your phone just can't get through at this time, ask your parents to contact the class teacher or your classmates.