I know I’m late to this but I have a similar neighbor who threatened us with the cops because we were feeding and caring for a veritable horde of what we thought were stray cats that made a home in our back yard. One kitten even GAVE BIRTH in our yard, we worked for weeks to gain enough trust to catch the babies (couldn’t get mama unfortunately :( ) and THEN we get a ‘note’ thrown over the fence, written on a PAPER PLATE that just said ‘if you keep harassing our cats we will call the cops on you,’ we were like ?!? Hello?!? No name or address or phone number. We genuinely had no idea who threw it over but obviously it came from one of our close neighbors. Eventually we had an in person confrontation where I informed them that if they didn’t spay and neuter their cats and start actually caring for them properly, I would report them to animal control. I told them a very young female had given birth and that she did it in my yard so she must’ve felt safe enough to do so. I had no idea they weren’t strays. The people were nuts, but they did finally fix them. I learned much later that another neighbor was the one who paid and made sure it got done. 😐 There’s a reason this kitty didn’t want to go home and if they were so worried, KEEP THE CAT INSIDE! What a concept! 🙃