Really rude roommate?

I'm a college student and live with others in an apartment, recently one of them moved a random guy into the apartment without asking anyone at all! I asked them about it and they confirmed what I thought had happened. I was on the phone talking about how rude it is to not have asked anyone, how I shouldn't have to pay rent because it isnt fair, etc, and they heard me and decided to talk on the phone about me infront of my door. I've been told to say hi just to keep things cordial, but they don't even look up, should I even try to remain civil?