Rental increase

My father and mother both senior citizen and stays in Kolkata in a old house which was build perhaps more than 60-70 yrs ago or even more. The house is in terrible condition and corporation has given all the tenants and landord one month time to get the repair done.The repairs are going on.My parents were paying rent of Rs.200 and then in 2016 around mid year the landlord wanted to double the rent which my parents didn't agree. There is no written rent agreement as my parents are living there for 46 yrs. .So my father sent the rent by money order in the month of September 2016, we still have that money order which the landlord refused. My father didn't submit the rent to rent controller as he wanted to settle the matter with the landlord. In between the landord died and till date no rent was paid. Now landord son is demanding rent as Rs.800 from October 2016 and it is not possible for us to increase so much rent which is 400% increase.Now what are the option my father has?.Can he pay the total rent due for 4.5 yrs at one time to the rent controller for RS. 200 each month? If so will the rent controller accept the rent now?Please suggest the best possible way to proceed with the situation. Thanks.