There are a few things to consider here.
Firstly, if you are being harassed and victimised and you feel unsafe then you should report this to the Police as a matter of priority. Even if the Police aren't able to do anything at this time, it is still best to report it and keep reporting things as they happen. This will help you to build evidence if you need to look at other legal options to stop the problem. i.e restraining orders etc.
Speak to your landlord. If you are a council or housing association tenant your landlord needs to know what is happening particularly if your neighbour is also a tenant of theirs. There is action that the landlord can take to prevent this happening.
If you have a private landlord, there's probably not much they can do about it but it's worth speaking to the landlord to see if past tenants have had similar experiences to yours. You can also speak to your landlord about increasing the security in your home to make you feel safer.
The best people to speak to about this would be Shelter, they are experts in housing law and if you yourself are at risk of eviction it's a good idea to get some advice about your rights. www.shelter.org.uk
If you want to talk some more, please get in touch. I hope that you manage to resolve this.