As per National Insurance Company Website -
"Cancellation of the policy may be done ONLY in cases where a journey is not undertaken and ONLY on production of the insured person’s PASSPORT as a proof that the journey has not been undertaken. Any request for cancellation will be entertained not less than 14 days after the First Day of Insurance as indicated in the policy schedule. Such cancellation will be subject to deduction of cancellation charges by the underwriters as applicable. Partial refund in premium is permitted on trip band basis provided cover is for a minimum period of 60 days and unexpired period is not less than 14 days subject to there being no claim under the policy"