Hi Sonak its me again, just a thought, do you know if your housing association has a secure or short hold tenancy agreement? where i live, new tenants sign a temporary contract for 12 months after which they would sign again for a secured tenancy. I know from our neighbours that if you continue complaining (by filling out the incident sheets) the housing association have to apply to the courts to get the tenants out. Make sure you keep complaining to the police, as they have a duty to inform the housing association. This also supplies you with a back up to your claims. Dont worry about the nfh throwing accusations back, stupidly, they have a right to reply to any complaint made against them.
Also, if your able, put cctv camaras up. Weve got them and although you cant film on your neighbours property, these camaras can pick up sound. So if they verbally assault you again, you will have the evidence on tape.
You could also go to your solicitor and see what they can do, maybe an injunction under the protection from harassment law.
Anyway, although this is quite frustrating, you know your not alone.