What to do about this nasty voicemail?

recently the boy i had a thing with hooked up with another girl at a party. that girl alexa is my friend. i was very hurt because of alexa but i didnt really care about the boy. i havent talked to her and i didnt make it a big deal and just brushed that incident off. i decided to stay friends with the boy but nohthing more. anyways today i got a nasty voicemail saying im a slut whore whatever from the guys best friend. and it really hurt me. i didnt even do anything and it sounded like he was drunk. i could hear alexa in the backround and a bunch of his friends. i dont know how to handle this situation. any tips?