Do you have a lease? What does it say regarding these situations. My lease spells this stuff out clearly.

I would go to the agent who you used when renting the property and ask them to get involved on your behalf. If it is a good agent, they will do this. If you cheaped out on the agent from the get go...then good luck!!

Also, when someone comes to the house unannounced tell them to F-off and close the door on their face. The landlord will get the message quickly.