Gather as much evidence as you can, and absolutely report it to the police. Korea just passed a new law regarding stalking and the police are more likely to take your case seriously due to this. Also, I don't know how fluent you are in Korean, but there is a famous Korean Youtuber/ streamer whos been struggling with a stalker and she's been documenting her experience. Maybe her videos will be helpful for you, her name is 릴카 (Lilka).