Tenant wants to sell the possession.

Sir, I am an owner of a premises at Topsia Kolkata. There is a small shop room rented out by the owner prior to my purchase.in 1997. He is running a hair dressing saloon. The tenant has been paying me rent regularly since 1997 and I have been issuing him rent receipt regularly. Now, suddenly he comes one day and says that he wants to sell his possession to some third person and orders me to change the rent bill in favour of the new incumbent. I told him that you are a tenant only and how can you sell the possession to someone else. He says that he had given salami to the previous landlord and has every right to sell off the shop to any one and I am bound to change the rent bill. On my refusal to accede to his proposal, he is now taking the help of some political looms who are rather creating pressure on me to accede to the dictum of the tenant. Should you need further details, kindly advise me. Sir, please guide me suitably. Regards, A Hossain email: husnaluv@gmail.com