First of all you may explain the matter in writing by letter addressed to TPA, Insurance Company, and Mediclaim Help desk/HR personnel responsible for interacting with Insurance Company and obtain a response from the company.
The discharge summary issued by the hospital must have details of the condition of the patient at the time of admission and treatment given in ICU and IPD.
Obtain the copy of Policy Issued by Insuarance Compnay to Company of your husband inclusing list of exclusions.
A certificate by the doctor who treated the patient at home, recorded the BP and recommended admission may also be referred.
The doctor who treated the patient in ICU/IPD can issue emergency certificate and explain the line of treatment.
The bill issued by the hospital give itemized detail of charges and charges for ICU and other room charges and several doctor visits should not have been rejected.
Let the company reply to you in writing.
In the meantime you may go thru
------------INSURANCE REGULATORY AND DEVELOPMENT AUTHORITY
(HEALTH INSURANCE) REGULATIONS, 2012
-------------GUIDELINES FOR GRIEVANCE REDRESSAL BY INSURANCE COMPANIES
-----------IRDA Grievance Redressal Call Centre Toll Free Number is:155255.
You can speak to them and understand the matter.
---------You may also get in touch with a lawyer specializing in Consumer matters and especially pertaining to Insurance. You can find out about lawyers from local DCDRF.
You may show all docs, give inputs in person, understand the merits before you proceed to file a complaint.