Well, I am a police officer, and as already stated by multiple members document everything, and if they do say something on a voice mail keep that. Dont know about your state as far as recording the conversation, but worst case scenario you just couldnt use it in court. If they keep calling make a police report, if they keep calling file a protective order against them and after a few times it becomes a stalking charge which can be a felony. Under no circumstances go back to that house, neighborhood, or even meet with them in any way, there are too many crazy people in this world anymore and I have seen things that started out smaller than this go terribly wrong, and it aint worth it. I commend you for your work ethic, dont ever lose it, and chalk this up to a learning experience. Unfortunately with the ethics a lot of people are raised with these days, it probably wont be the last time you deal with a jerk. Also as stated earlier get a walk around agreement from now on. The days of a handshake agreement, or gentlemans agreement are probably over unfortunately. Remember common sense isnt common.