When I was a kid, I was smaller than the others and so I was bullied a lot. The difference between then and now is that I am ready to go to the authorities when I'm bullied. In school, it wasn't cool to go tell the teacher or the principal. In the adult world, the police are authorities just like teachers and principals. Your power is your unwillingness to let the bullying continue.
Bullies play on fear.
They enjoy it when someone is scared of them. If they know the consequences of their actions will not be good for them, then they'll leave you alone. Tell a teacher. Tell an adult. Tell the principal.