Orphan property in delhi :(

Fate of the  commercial shop undisputedly occupied by me for over 12 yrears in heart of Delhi .  Actual tenant was my father since 1950 till death in 1970, and had paid the rent till then and later by me upto 1990.
After that till date, the legal heir of the actual owner has not truned up to claim the rent and have been avoiding all approaches by me.  The heir has turned Saadhu and has disowned legally his son and wife, as per the information known to me and the heir is not interested to claim the rent and also sell off the property to either me or anybody.   
Under such circumstances how I can become the owner and sell the shop. Please guide.