ONGC — to claim unclaimed dividend

Address:

Mumbai City, Maharashtra, 401107

My name is shalini deewan, i am the daughter of late mrs kamlesh udaybhan singh wife of mr udaybhan singh who was an employee in ongc. My father died on duty in 1994, after that my mother got shares then she got dividend which is unclaimed till now and after 2007 my mother didn't got any more dividend and my mother also died in 2014. So how can i claim those unclaimed dividends?