My father has a rented shop from past 30 years

Sir my father has a rented shop from past 30 years but we dont have rent receipt because earlier it was with my grand father he used to work there and the landlord was like a friend to my grand father so he never asked him for rent receipt and now the land lord and my grand father both are no more and the shop is now with my father he continuing the same business there, before one year one of the brother of landlord told to my father to vacant the shop and he also offered some amount of money to my father to vacant the shop and my father agreed to his proposal, but now few month before one of the son of land lord came to my father and asked to vacant the shop, but he offered only 25% of the amount which was offered by his uncle.My father still doing his work there and paying rent regularly and now when my father asked him for rent receipt he denied for that and said to my to vacant the shop. So in this situation is there anything in law which can give protection to us because we have only that shop to earn our livelihood.