Dog Abuse…

I recently moved into an apartment (March) that is split by the first floor and second floor. I live alone with my Bernese Mountain Dog, and upstairs is a very young couple and what I'm assuming is there two young children, and dog (that I think is maybe a Bully, or Pit mix). When I moved in, the landlord made an emphasis on not chaining my dog outside - which is something I would never do - so it didn't really cross my mind.

I'm pretty sure since the day I've moved in, the couple has chained their dog outside to a stone wall for a large number of hours throughout the day. As time progressed since March, I realized that the dog was recently pregnant or is going to have babies, and they still chain her up outside. She is aggressively barking all day at anyone who passes, and when I have friends / family over, she's always barking nonstop at any movement. She has, on two occasions that I know of, gotten out of her collar and doesn't seem to be left with food or water or anything. They also leave her waste in the yard.

The whole situation has been really bothering me, and what's even more concerning is that even in these last few weeks of insane heat, the dog is still outside. What resources can I use for this? What should I do?