Dowry harrasement

Hai sir., my name is Anil Kumar., Iam writing this to you regarding my sister problem., sir my sister marriage was done on 07-12-2014, on the day of marriage they qurraled with us for the remaining balance dowry., as per written agreement total dowry was 5,00,000/-(2,00,000/- should be given before the marriage, 2,00,000/- for gold, and 1,00,000/- after my father retirement), as per the written document we gave 1,00,000/- before the marriage., they asked us to take the gold for more 50,000/-., the balance left was 50,000/-, but on the day of marriage they took 50,000/- cash, 50,000/- cheque. We do have original document what we have written before the marriage. After marriage they(father-in-law, mother-in-law, husband & sister in law) started harassing my sister mentally and physically. Now we are looking to punish those people by lodging a complaint in the women's police station. But we don't know how to write a complaint which should be very strong., those people should be punished. Please help by giving or mailing me the letter format. Thanks in advance....