Help, My neighbour who owns a flat above mine , keeps her stray dog right outside of my door.

IDK how to write this but I'll try . So I own a flat in a building which has three floors. Each of the flat belongs to a different owner. Mine is on the first floor. I'm having a dispute with the people living up stairs . So basically this person and I share the same stairs and theres a small balcony outside my door which is most probably a shared space too, and this person keeps a aggressive dog right outside my door beside the stairs where the balcony is. I've asked them since last year to remove the dog as I'm constructing a restaurant in my flat . They don't remove the dog , they don't give him to a shelter or keep the dog in their house. It's a stray and they don't even have a license for the dog . This dog has attacked 2 of my workers and I had to pay 9k for their vaccination. Is it even legal to keep dog outside my door in a shared space. If I let the dog be I'm sure no one will pull up to my restaurant . What can I do about it??? this person even threatened me that they'll build a big gate at the entrance at the ground floor . And if that happens how will I get to my flat as that's the only stair. HeLP