Need help! Video and audio of other students and teacher don't work

Hello there, I have a problem with jitsi for almost two weeks now. Our support teacher and my father can’t find any solution for it. My new laptop, my one year old tablet and my 3 months old smartphone can’t recieve any audio and video data from teachers and other students. They can hear and see me without any problems. I tried it with the Jitsi App, with Firefox, with Chrome and Opera and it still doesn’t work. Other programms like Zoom or Skype are working without problems.
We reinstalled the webbrowsers and searched for blocking programms or mistakes in the server and the three devices. I need as fast as possible help because I am getting problems with my school principals.
Edit: On my father’s computer and his laptop and my old dead laptop it works/ worked.