A little help would be appreciated?

there is a girl...my ex girlfriend that is obsessed with me,she keeps stalking me and threatening my girlfriend that she is gonna beat her up,she is a real noosence i dont even like her infact i utterly hate her and she keeps saying stuff to me like i love you but she keeps telling people lies and bad things about me....pls tell me how to get her of my back its what i want for my birthday,new year,christmas anything i just want her gone....