Tenancy

In 1979 my father(a Hindu), had given on rent @300/- a godown to a firm having 4 partners for mfg. and trading in Kolkata. Agreement was signed by all four partners having equal share. In 1985 one partner retired. In 1995 a new MOU was entered, whereby rent increased to 800/- with a clause of 10% increment every 4 years. This agreement was signed by one partner who held 50% share. The partnership firm was converted to proprietorship keeping the firms name same without informing us which I came to know a couple of years back. The Proprietor of the new firm(was not a partner earlier) is the son of the partner who held 50% share in the partnership firm and is still alive. The firm used to pay rent by cheque which my father used to deposit in bank. In 2013, my father expired. At the time rent was lying unpaid since past 6 months. I have not taken any rent from him after my father’s death and there had been no agreement with the Proprietor of the firm. The property is in the name of my late father. I am the sole legal heir. What should be my legal stand? Should I go for fair rent or can he be evicted since there had been no agreement with the proprietor of the firm and my father?