I don't know who works downstairs Every eleven or twelve o'clock, the songs are so loud that people can't sleep. What should I do?

If it is the noise of the audio equipment in the residential building, you can call the police according to the relevant provisions of the National Noise Pollution Prevention Law. If you are not sure which one it is, it is recommended to report it to the property first, and ask the property manager on duty at night to help determine which one it is or convince the property first, and then call the police if it is invalid.