Which department does the census work belong to? Is it reasonable for the neighborhood Committee to hand over all the door-to-door work to the property?

Unreasonable. Property companies are only obliged to assist neighborhood committees in conducting population census. Since it is helping, it is mainly based on neighborhood committees, supplemented by property companies. What the neighborhood Committee did was to interfere with the normal operation of the enterprise. You can report to the Housing Authority. If the Housing Authority doesn't care, you can directly call the mayor's hotline 12345 to complain.