This is what your neighbors must have done: They called DFS (Division of Family Services), the caller's name and phone number appears on DFS worker's phone but your neighbor must have told the hotline staff, "I want to remain anonymous."  The person taking the call is ALWAYS different from the person who comes to investigate.

Anyways, is the pay back really worth it? What if your neighbor calls INS? You may lose in the long-term.

Can't you move? Or ignore them until your lease ends? What you can do is call the police multiple times complaining of the loud noise. I am sorry to hear you are going through so much trouble.