Sharraxaadda

Neighbors won’t clean up the feces from their 3 dogs that use the small back yard only(never walked). It smells so bad I can’t use my yard. Since my yard is down hill I’m also worried about the run off into my yard. There are lots of flies too, which is definitely not sanitary either. I have asked them to clean it up on several occasions and they say they will not. It’s only dirt, rocks and feces on the ground, no grass. Who do I speak to that can help me?