The best way to deal with bullies is to collaborate with others. Don't try to deal with bullies alone.
Some schools have adopted restorative justice to show the damage that bullies do to the kids they bully. They set up a meeting between the parents of the bully, the parents of the victim and the bully and victim. Then they have a nice chat to talk about how each of them feels.
Once the bully comes face to face with his victim in the presence of other adults, and he can see how the victim feels, most of the time, bullying ends. Not just because parents on both sides know, but both kids understand each other a little better.
https://www.stopbullying.gov/blog/2016/03/02/restorative-justice-practices-and-bullying-prevention
Exactly @digitalfirehouse very well said. There must be a presence of both parents to resolve this peacefully and also to understand the cause of bullying.