Indian Overseas Bank — they are not responding properly for death claim without nominee

Address: Bangalore, Karnataka

My dad expired and there is no nominee for his account.. V want to claim the mny in his account but iob bank ppl are telling we want family tree from thasildar office if we go for thasildar office and ask fr t thy are telling it's issued nly for govt sector employees bt my dad is private sector employee and i have fmly tree from notary thy are not ready to accept it.. Now what should i do.. Can u please help me