Mostly a south Indian festival, Vishu is the dawn of a new astronomical year, and the day marks the first day of the Malayalam month of Medam that corresponds with April in the Gregorian calendar.
They will issue a refund and depending on the method of refund, this should be completed within 28 days. You will be asked to return all documentation regarding the gap insurance you have cancelled and the cover will cease at this point.
The official website said that it will take less than 21 days to receive the refund after the filing of the tax returns. So better be cautious about the 21 day period.