Remedy against residents of society encroaching into private premises

Hi Sir/Mam, I bought a house last year and all the procedures including registration and Khata transfer has completed successfully. We are having 3 gates 1 gate at back side and 2 gates at the front of the apartment for easy access to both backside and front side of the apartment. But off late outside vehicles and other party vehicles are using our premises to move from the back side to front side also the other residents staying in and around our society is also using our society's facilities as their own. All this is happening because our society is located at a high land and other land owner had an agreement with the land owner behind our apartment that he can allow the water seepage down his land provided he allows the residents to use our premises. So we are now stuck from closing the back door making our resident virtually a security hazard. How can we get out of this situation as we were not informed when we bought the apartment from the builder. Thanks,