How can I update records without the deceased's death certificate?

I own a house purchased 10 years ago, before Aadhaar was implemented, from someone. Afterward, the legal heir (his wife, who was originally allotted a housing board house under LIG) inherited it following her husband’s death. The AP Housing Board Executive Engineer registered and executed the sale deed in her name. Now, I want to update the mutation records in GHMC, as well as for electricity and water bills, but the bills are still in the deceased person's name. The GHMC officials are asking for the death certificate, but we don’t know their whereabouts. Kindly advise how to proceed further.