The father of a college student at the university where I am employed is threatening and harrassing me. What can I do.

This student told her father fabricated stories about her experiences in my class. TThis lawyer has sent harrassing and threatening emails and voicemails to me, my boss and college administrators. These unsubstantiated accusations have been deemed untrue. What action can I take to force this lawyer to retract his untrue sttements and submit a written apology?