Problem Tenants in Same Stairwell

Other

I have an apartment which has communial stairwell. Most of the apartments are rented. The tenants in the flat across the stairwell are causing a lot of problems upsetting my tenant and others.

1. There are keeping a noisy dog in there.
2. Throw rubbish out of the windows.
3. Always having noisy domestic arguments.

The apartment causing the noise is managed by an letting agency who seem to want to keep the tenant and money coming in.

The company that manages the communial areas has been involved but only in writing letters to the flat.

I know my tenant who is great will give me notice soon as he's fed up with the noise.

Which is the best way to resolve this. Is any legal action available against the letting agent ?