Dowry

Respected lawyers i want to ask about the case of my sister. My father had fixed the marriage of my sister to a boy residing delhi.At the time of marriage fixing both the families discussed all the details of both families.we have done all the preparations of marriage and we expanse about 3 lac in ring ceremony and bookings.But before around 20 days of marriage the Boy and his family started asking for money and luxury car and lot more things to my sister and mother over phone and whats-app msgs.And also started mentally torching my sister.They abuses my parents also and said if you can not fullfill our demand so we are not ready for this marriage.we distributed the invitation cards also.Looking at their changing nature my family has decided not marry to him.we have the proofs of asking for dowry.we also gone to police station to lodge a FIR but the police says there is no such provision to register a case like yours.They are saying there is no section and rule under which we can do any proceedings.Now the date of marriage also has been passed .So please give your suggestions what to do and under which act and sections we can file the case.