If the police witness or have probable cause to believe that the defendant violated a harassment prevention order, they have to arrest the defendant.
A harassment prevention order is a civil order, but violating certain parts of the order is a criminal offense. If the defendant violates the no abuse or harassment, no contact, or stay away from home/work terms of the order, you should contact the local police department immediately. Tell them that you have a harassment prevention order and explain what happened.
If the defendant doesn’t pay any money the court orders them to pay, you'll need to go back to the court that issued the order and ask for a hearing to see if the defendant should be held in contempt of court.