PKash, my Non-availability certificate issued from a panchayath in Kerala ...
... is on a pre-printed form with heading:
Form No. 10
(See Rule 13)
NON-AVAILABILITY CERTIFICATE
(Issued under Section 17 of the Registration of Births & Deaths Act, 1969)
So, surely there is a Rule 13 which authorizes a Form No. 10, which is the NAC.
Otherwise also, official communication is not by verbal means. It has to be a written communication. If nothing works, send an application through a lawyer and it will not cost more than what these idiots expect you to shell out to "grease their palms". Let it be official!