Regarding insurance claim

Dear sir/Madam,this is selva from chennai.I had filed a claim,for medical reimbursement of my father's hospitalization in Dec-17,with the New india assurance company.The claim amount around 2lakhs.My insurance policy is a group mediclaim policy,given by my corporate. The reason for hospitalization was heart dysfunction(which developes multiple organ dysfunction),which is due to sudden severe heart attack in nov-2017.But the claim was rejected by the insurance company.They given reason ,that in hospital ICP,Patient had the alcoholic history,chronic alcoholic liver disease were mentioned .so they told they rejected claim on alcohol Grounds.Though my father has the alcoholic history,he completely stopped alcohol for last 10 years.It was also mentioned in hospital ICP. In the reply letter for the rejection ,treating doctor clearly mentioned that,that admission was for heart ailment,moreover patient stopped alcohol for 10 years.so the Dr. recommended that claim for reconsideration.But still insurance company refused the claim. [moreover my father passed away on Feb-2018,due to heart failure.] on the otherhand the same insurance company Approved the cashless claim upto75000 for my father for Liver disease in 2015.Same insurance company also gave reimbursement of 25000 for my father in 2014 for liver ailment. I dont know why they are refusing the claim now,for heart ailment? Dear sir/madam, kindly guide me how to get my reimbursement amount,from insurance company.