If he is calling on your mobile phone then just go to police station and show your mobiles call history to police station. They will directly assist you to file a complain and action will be taken directly and this guy will be behind bars in minutes.

If he is calling on your land line then go and file a complain in police station. They will request Qtel to monitor and record your land line conversations. Sure next time he calls he will be caught red handed.

Good Luck

Peace