Help with a title

Please, I can't remember the title of this movie I saw a couple of years ago, probably around 2008-2010, and around those years this film was too.
It was a korean film about a young man who tortured and killed prostitutes. He kidnapped this young woman (prostitute) who had a kid, she was sick but her pimp sent her anyway. Long story short, the pimp looked for her at the same time he was watching for her kid who finally ended up in a hospital. She managed to escape his captor but well, the ending is very frustrating. Anyway, I have had a hard time trying to remember the title or the actors, I thought the main actor was Kang-ho Song and I reviewed his filmography but couldn't find this particular movie.
If someone can help I would be forever thankful.

English not my first language. Thanks!!!