First a representation should be written to the Insurance company and if reply is not received within 30 days a complaint can be lodged before the insurance ombudsman.
The procedure to make the complaint is below:
Manner of lodging complaint
The complaint by an aggrieved person has to be in writing, and addressed to the insurance Ombudsman of the jurisdiction under which the office of the insurer falls. The complaint can also be lodged through the legal heirs of the insured. Before lodging a complaint:
i) the complainant should have made a representation to the insurer named in the complaint and the insurer either should have rejected the complaint or the complainant have not received any reply within a period of one month after the concerned insurer has received his complaint or he is not satisfied with the reply of the insurer.
ii) The complaint is not made later than one year after the insurer had replied.
iii) The same complaint on the subject should not be pending with before any court, consumer forum or arbitrator.
For further details visit the below link
https://www.irdaindia.org/ins_ombusman.htm