House name stolen by neighbour

Hi,

My house name is Castle View and our next door ‘neighbour’s property is called Ysgoldy. They moved in around 2 years ago or so and immediately started displaying “Ysgoldy Castle View” on their property which is causing dramas with post, couriers and anyone else trying to find my house. They insist that their deeds include Castle View but refuse to prove it. 
I have asked them to stop using it which they also refuse. Where does this leave me legally as I have concerns they are going to try pushing their boundaries into our land. 

Thanks in advance 

Hi Simon - a Q for a legal adviser and not HMLR I'm afraid
Postal addresses are controlled by the local authority although I don't think they 'police' them in so far as someone displaying an alternative on their property
Very much legal advice you need here re what your options might be