How do i report someone on msn?

Yeah i understand u can block them, but this person has added all my mates its obvious it is someone we all know but we dont know who, there calling my mate fat and other names and i dont even no why as she anit did nuffin wrong, therre doing it to other people n thinking they can gett away wif it. its basically cyberbulling right? so i wanna report them how do i do this?