I'll have to speak with the police again about them..
Ask the police what you can do to help them put a stop to the problems. For example, often catching them doing some activities are more likely to result in strong action, so just knowing what to call on is a help. Once the police know there is a problem in the area, they are often desire to be able to stop it as you do but just need help (and a bit of luck) to be able to.