Rajeev - From which PSU company, you had bought the above mediclaim policy?
It's not same for all insurance companies. Main rules of PSU mediclaim are below -

The No Claim Bonus is also called as Cumulative bonus.

Cumulative Bonus will be available under mediclaim policy subject to the following conditions -
1- Sum Insured under the Policy shall be progressively increased by 5%, by way of cumulative bonus, in respect of each claim free year of insurance, subject to a maximum accumulation of 10 claim free years.
2- This cumulative bonus is applicable to the sum insured, which is renewed continuously for a period of 3 years including the current year. In other words, the cumulative bonus will be applicable on the least of the sum insured during this 3 year period.
3- For fresh customers who are already covered under any other mediclaim policy, the cumulative bonus, if any, earned by them earlier, shall be allowed upon continuous renewal under this policy subject to a maximum of 5% only.
4- For renewal customers of Good Health Mediclaim policy, this cumulative bonus would apply effective from Oct 2004 GH scheme only subject to a maximum of 5% in the first year provided there being no claim during 2003-04 policy.
5- In case of any claim under this policy in respect of the insured person who has earned the cumulative bonus, the increased percentage will be reduced by 10 % at the next renewal. However basic sum insured will be maintained and will not be reduced.
6- Cumulative bonus will be lost if policy is not renewed on the date of expiry.
7- The Cumulative bonus shown in the policy certificate is provisional and it is subject to revision in the event of any claim under the earlier policy being reported after issuance of this policy.

Source - NewIndia website