I cannot really give any well founded legal advise, but reading the OP's post, I am wondering about the following: Why the heck does the landlord know where you work? And why would you care if the landlord tells "everyone in the building" that you have not paid rent - and for that matter why would anybody who is told about this give a damn?
I am also not sure about the building security arrangements and what are your relations towards them vs, the owners, but I would inform the reception staff that you don't want the landlord to enter without your explicit consent.
If they manage to enter anyhow and bang on the door as you experienced, immediately call the police again or if feasible, just ignore it - maybe some neighbour who is annoyed will take care of it. If you know 'someone' who could be atr your unit and tell them in a friendly way to get lost, that might also be an option.
Overall, from own experience, if you have a toxic landlord, move on, there is little to gain from fighting back - it just eats up too much of your energy.