How to make a Complaint about a neighbour?

Not even sure if this is the right sub but I’ve been having a an issue with my downstairs neighbour and can’t get a clear answer as to where I need to go to file a complaint with the local authority as there was an incident this morning with some creepy behaviour towards my partner. My landlord won’t point me in the correct direction and I’m genuinely struggling on google to find the correct place to go hoping this shot in dark may help.