Falling

This happened a few weeks ago. I've been ignoring it and hoping my neighbour would fix it. Nothing happened. The neighbour is renting the flat and when I spoke to her, she said that she showed it to the woman who owns the flat. The flat owner said she doesn't know who owns the fence. She spoke to the family living downstairs who said they thought it was my fence. 

I've checked all my paperwork from when I bought the flat, nothing about fences. I've paid to download the info on the Land Registry about my flat. Nothing. My neighbour downstairs who's lived there since the 80s, thinks it's not my fence. And the last time there was a problem with it (several years ago), the then owner of the next door flat fixed it. 

Hmm, how to prove who owns the fence?