He's playing the system against you. Of course he deserves a good kicking but you can't do that. What you can do is play the system against him. You can't talk to him but you can talk to the people to whom he complains. This makes you friends because you don't ask anything of them you only give then useful information that makes their lives easier next time.
You've made a good start with the animal welfare people. They've been to see you (again), they found there wasn't a problem (again) and they've been helpful. You've won this battle and you've reinforced a relationship with people who matter. It's a success for you and a kick in the nuts for him, so have a drink and smile a bit.
OH has a technique for smiling sweetly at people who are being complete c+++s while saying things that make them foam with rage. Smile while the other guy loses it and you win.
We're here for you.
Simon