My neighbors are dumping their garbage in my garbage cans. Are they breaking any kinds of federal laws?

They dump all their garbage in them and I have no where to put mine. They live in an apartment complex that should have trash chutes or some kind of dumpster. They have easy access to my garbage cans so I can see why they would use it, but it's MY garbage can! I've tried talking to them, but all they give me is attitude and they deny it. what am i supposed to do then?