Recovery of property given under oral agreement

My parents purchased two house properties located together, in the year 1993 under a power of attorney issued by the former owner. Our family has been in possession of the said property since 1993. However the ownership of the property still vests in the name of previous owner. And even today all bills come in his name. In 1995 Our family demolished the houses and built a single house on the combined property and we have been using the same .. in 2015 my mother gave the said property on rent to a person for running a school under an oral agreement, on a monthly rent of 10000. For last 6 months we have been communicating with him asking him to vacate the premises. Last month a member of our family paid him a personal visit to ask him to vacate the property. Instead of vacating , the tenant has filed an application under rent tribunal, alleging forced eviction, and asking for maintainece of status quo. He claims that we signed an agreement with him where in we agreed to mutually renew the contract of lease every three years. Also, he has stated that we have agreed to an upgrade of rent by 5 percent. How should we proceed?