My Strange Hero and also Moment at Eighteen deal with bullying as part of the story, although I consider the main themes more to be overall school pressures. Both are very good dramas if you haven't already seen them.
Since you've already seen everything previously mentioned, I imagine you probably already saw Boys over Flowers which is about a bully main lead and the little spitfire of a girl who stands up to him. Imperfect, dated, and over the top but a fun watch regardless, no matter which version you watch.
Another is Solomon's Perjury which deals with an in school trial process after a student dies and there are questions about how the student died, one of which is that bullying may have gone too far. I found the acting to be strong but it was a bit boring to me. A lot of others did enjoy it more than I did, so maybe you might like it too.
