As you are in West Bengal, I think it will be the Urban Area Rent Control Act that will be applicable in your case.
First let me point your part of the fault before condemning the landlord. You said that "and also invested on some infrastructure of this flat". You cannot do that. It will be a violation of your Tanancy conditions, until you have a written consent to do so from your Landlord.
Now about the greedy landlord. The Landlord cannot increase the Rent @ greater then maximum 50% of the previous Rent, that also only after five years.
When you will be a "Tanent at Sufference", i,e after the expiry of the Rent agreement, You can deposit the Rents at the Court, And also if you can get the rent fixed by a rent Controller, you will get a relief of having to pay the fair rent for the building. "Fair Rent" is neither for the Landlord, Nor for the tanent, but for the Building itself.
But BEWARE, even if there is a saying that the Rent Control Act is in favour of the Tanents, there are lots of LOOPHOLES in the Rent Control Act that provides HIDDEN SUPPORTS for the Landlord to win, as the landlord IS THE REAL OWNER OF THE PROPERTY.
Ultimately, the Court may Direct the Landlord to Renew the Agreement with you, or you may get evicted as a Defaulter (If you fail in paying the Rent).
Hope you don't spoil your Time, Money, Peace of Mind & the Next 20 years in trying to settle such a case. Landlords never gives up even if they have to fight with Tanents for five generations.