How do I deal when no one wants to believe me?

Looks like you have tried to correct options (the direct approach, the landlord, and the police). Keep with those, and if you think you need proof then get it via a video camera. It has got to be frustrating. One thing that you may consider, is talking to the landlord again, tell them that they need to take meaningful action or you will pursue breaking your lease (without any penalty to you) on the basis that the landlord is not providing an acceptable environment for your continued living there. You should read your contract carefully of course. But that approach may send the message that the landlord needs to rectify the situation. That is the only other peaceful and legal option that I can think of. The police can also pursue any legal infractions that may be occurring - many localities have noise ordinances. You can ask them what you need to do to give them enough of the pertinent facts to pursue that angle. Best of luck to you.