You can sue a person despite that the contract is unregistered. In the prevailing situation you have a right to recover the rent of three months along with interest and also claim damages. This house was let out for three years. If the term of lease is more that one year it must be registered as per the provision of section 107 of the Transfer of Property Act.
Registration of lease agreement was mandatory. When the registration of deed is made mandatory by law, and not registered that deed shall not be admissible in evidence. But it tends to show that parties were entered into an agreement. On the basis of agreement, you can sue him for the damages and recovery of rent. For more legal help please visit Kanoon India.

