Harassment of a girl by phone

I have a friend who is been constantly mentally harassed by an old college mate.He has the possession of the numbers of her family numbers and is blackmailing her into talking to her all the time . He has cooked up stories about her being in a relationship with him. From what I understand he has "imagined" that he has been in a relationship with her. He is currently forcing her to get in a marriage with her. He has threatened that he would call up her aged parents and sisters and other relatives and defame her.He has once tried to cut his hand for silly reasons . How much ever she tries to keep away he comes back. He has also said he knows the address of the office , and he can come and defame her in office as well. He once talked about the usage of acid in an indirect way. He is currently in a different location as of now. He was friend who turned into this "psycho". How can she solve this menace permanently ?