Rule on accessing the bank account details of my deceased husband

Hello My late husband has a account in PNB which i was on aware of unless recently. But that account has last transaction of 2002, 3 days before he died.So i went to the bank with passbook for information but they were unable to find the account as its a long time now and the account no. was of only 6 digits(nowdays account numbers are of 16 digits). Finally they said my husband must had closed the account. So i asked to show me the record? They refused stating that its a long time so there are no records. Then i filed the RTI asking to provide new account no. assigned, status and other details of the account. Now i received a reply that they cannot provide the information as i have not presented the death certificate, legal heir certificate and NOC from all other heirs. Ok this seems justified BUT please note that in RTI i was not asking for the settlement of any claim nor i have mentioned anything about balance. I was just asking for account details which the bank was unable to provide in first place. Asking for information as citizen of India, legal heir and affected party is different from asking for settlement of claim. So now i am going to send my husband's death certificate along with rashan card copy and a affidavit stating proff of legal heir. I have no problem with that but i want to back my side by adding any RULE/CIRCULAR/DECISION stating that EVERY LEGAL HEIR OF DECEASED PERSON HAS THE RIGHT TO ACCESS HIS BANK ACCOUNT INFORMATION. Sorry for the long post i wish i could explain in less. Please provide the rule if any. Thank you