Which department should I find for the illegal renovation of residential stairs?

The property has no law enforcement power, but the property can report to his superior, that is, the real estate department, that this is an act of changing the structure of the house without authorization, and the real estate department can order those who violate the rules to restore to the original state and punish them in accordance with the property management regulations. You can also complain directly to the real estate department. If the real estate department handles the delay and prevarication, you can not only continue to complain, but also bring a lawsuit to the court in accordance with the general principles of civil law because the stairs in the community have been illegally transformed (the evidence affecting your interests must be sufficient).