If a/c holder has filled nomination column in the a/c opening form then nomination shall be registered in register and nomination number, date of nomination, nomination registration number is entered in the pass book of RD, MIS, Saving a/c under the signature of postmaster. In case of NSC nomination registration number, date is entered on NSC.
You may refer to the a/c pass book and check the details. If PO has not entered nomination number and nominee details in pass book you may submit a representation under acknowledgment to the Sub Post master/Post master and seek a written reply by registered post so as to reach you say within next 7 days.
Thereafter you may approach Post Master General of your city with a written complaint and seek redressal of your complaint and process to obtain copy of a/c opening form, nomination registration form ( if nomination was made later), to draw the payment by legal heir of the deceased. PO must be having a well laid deceased depositor policy. On your complaint Po is duty bound to block the payment.
You may also approach DSO ( Dist. Savings Officer) of your city.
Some of the forms/policies are enclosed. However you may obtain prescribed forms/formats in use from PO/Post Master.