House occupied by tenanted children and denying to vacate

Dear sir 8.months back we have given rent to person who is working for bramhakumari seva good person. His son and daughter in law kept illegal activities on him and he left our house. His son and daughter in law occupied with out any information to us. As per rental deal we told to vacate and given prior two months intimation. When we informed police officer that they are not vacating police officer said we were not authorized to get involved in civil case. The next day our tenent son and daughter in law They don't only vacated our house and put a case of harassment against us. We inform to police station that they are not vacating our house police officer told we are not authorized to make them vacate it's a civil case. They don't have any agreement with them. Please suggest a advice will be thankful for all