Dear Mr. Kumar,
Perhaps the PSU Company in which you were working is following the old pattern of receiving a claim and a "No Dues" certificate, after which they process Gratuity payment. You should first ensure that you have filed your Claim in Form - I. If they do not make this form available, just submit your claim on plain paper and obtain a receipt thereof. However, they cannot deny payment within 30 days of its being due merely on the ground of non-receipt of the Claim and No Dues certificate because Gratuity cannot be attached to any penalty or Court's Decree unless the amount is deductible due to termination on the ground of moral turpitude and the amount of recovery is mentioned on the Dismissal Order.
In case a period of 30 days has elapsed, you can submit an application to your office claiming interest on the payable amount for the period of delay until it is actually paid. If there is a refusal, you can approach the Controlling Authority under the PG Act, i.e., ALC(C), under whose jurisdiction the Unit of the PSU falls.
Hope you will get your dues as directed under the Act.
AK Jain