

Go to the landlord and provide your account of what is happening. Document as much as you can, and stop trying to figure out why they are so upset. You’re not going to discover some hidden rational explanation, nor is that your responsibility. Protect yourself.
“Legal” is also a bit fuzzy. Some countries frown upon copying an artist’s work, but that’s going to be a question for the manufacturer. Owning a reproduction is not illegal as long as you don’t try to commit fraud with it (i.e. hanging it in a gallery or selling it).