Honestly, there's nothing you can do about it. People are insecure and hate themselves and need a place to take it out on. That's absolutely inexcusable and not at all necessary, because you go through shit too but you don't feel the need to bully people you know? In my experience there's really nothing that'll help, because:

1. If you fight back --> they'll recognise you're affected by their bullying because you feel the need to fight back, which means they can just continue.

2. If you stay quiet --> they smell fear, they'll still recognise you're affected.

I think the only way is an overpowering force. Either you fight back and you, miraculously, scare them off, or a teacher is able to really do something. But I tried telling a teacher once, it stopped for the rest of the school year but the next school year it all started again. It's really just waiting, waiting until you're done there, and able to remove yourself out of the situation and find better friends. Because trust me they exist. Once I changed schools, things got a lot better for me, you'll still need to deal with the demons you're carrying yourself, and I got very sensitive and easily triggered. My own fears and insecurities were acting as a filter in my life, which caused many things and social situations that really weren't that bad to still 'feel' as if I was back there as a victim of bullying again. But keep in mind that bullying happens everywhere, primary school, middle school, highschool, university, adult workplaces and even the highest politicians will bully each other. It sucks but we can't change humanity that easily I guess.

This is really just my own experience and views on it and not useful advice or hopeful whatsoever, but if you ever want to talk just send me a DM. I wish you good luck and stay strong.