Non payment of maintenance

The Association, not being registered, need to move  the court of law for restraining the trouble makers.

Being unregistered the "association" can neither sue nor be sued.

You can report the matter to police and /or civil court for nuisance created against any one of the resident.

Consult a local prudent lawyer for profesional advise and necessary proceeding.

There are 12 flats in your building.  3 of the flat owners are giving problem.  Let 9 of the flat owners form an association. Amoung the aim of the association should be to form an association under any of the specific laws available to flat owners  in West Bengal.. Register the Association of 9 members. Legally write to the 3 flat owners to become members of the association. If they refuse, file a case in a civil court to order them to become members. All the common services should be managed by the 9 member association. Deny the services to the 3 members. I do not know what are the laws available in West Bengal for forming such an association. You may even form a co-operative society. The procedure I have given is general. There can be variations. Get a lawyer with creative thinking.