Someone called me and said we need to have a little talk, buh-bye. Then they called again and left a voicemail and they started screaming. What do I do?
You cannot trace this by yourself. It is private. But, if they called on private, it is most likely a prank. Don't worry about it,
If they keep calling, tell them you will contact the police and have them tracked down. (Which I believe they can.) That will scare them off, since prank calls is illegal.
tracing private calls