What is the procedure to file a defamation case

We live in a society where the association was formed and there was a discussion in the AGM on the method of calculating the maintenance amount ( 1) Sq.ft., 2) Hybrid and 3) Flat method), It was decided to collect the maintenance fee as per the Hybrid method through voting in the AGM meeting. A particular group of people was not ready to pay the maintenance amount in the hybrid method and they just paid in Sq.ft. basis which is lesser when compared to the hybrid method. This gave rise to the shortage in the maintenance collection, which in turn affected the payment to the vendor and the payment of the common usage EB bill. For nearly 4 months they are paying in this way and threatening all the other people of a particular block who are willing to pay the correct maintenance fee. In what way we can deal with these kinds of people and what legal action can be taken against these people. Is there any way by which the association can penalise these people? In the above situation, my husband has asked for the defaulter's list to the association in the official telegram group, and now one of the person, who belongs to the above category in the above case has filed a complaint against my husband, and two more people saying that they are threatening him to pay the pending money. In fact both my kids are going for tuition at their house and we have no clue why he did this. Now the police called yesterday and asked my husband to come to the police station. Today morning he went to the police station, the policeman was very rude to him and told him that the policeman has received a complaint stating that my husband is harrasing him to pay the maintenance fee. Not sure what to do in this case, my husband is innocent, tell me how to deal this case and tell me whether we can file a defamation case against him, and what is the procedure to do this ?