If the complex or the police don't do anything, I highly recommend this:
(Takes a 9 volt battery, not included)
Especially if the dog is loud.
I bought it, and while it can't detect the dog downstairs (smaller dog, quieter bark) it does react to me tapping it lightly to generate the high pitched noise.
I taught the downstairs dog it's not allowed to bark while I'm home anymore in about 2 days, probably half an hour total time spent.
I used to have the same issue with a downstairs neighbor, she had a little yappy dog that would bark in 1-second intervals constantly whenever she wasn't home.
I mentioned it to her and she apologized and said she didn't realize. It was fixed for a day or two but then went right back to the way it was.
So I bought this thing off Amazon:
It doesn't always react to the dog's bark because I think it's too muffled but it's pretty easy to trigger it by tapping the side or tapping it on the counter.
That woman has since moved out and was replaced by another woman with a larger dog who thankfully only barks when there's people right outside the apartment but I still use the box because it takes a while for him to stop.
Not foolproof and probably not a permanent solution but it might offer some temporary silence.