Tenant neither payment the increased rent nor vacating the house

My Parents are elderly citizens (55+). We have two portions of our house which is rented. Our main income source is from rent. In 2014 Mar my father rented out the second floor for a rent of Rs 10,000/month and with a verbal agreement that the rent will be increased to Rs 12,000(which was initially quoted and reduced for the first six month since the tenant pleaded that he needs the house urgently and is facing a difficult time in terms of income). My father who is humble and helpful in nature agreed to it without any proper agreement. Now after Six months , In Sep 2014 when my father told the to vacate they are not vacating the house