I am in no position to offer advice on legal matters, because I'm not a lawyer or anything. But I would say that you need to get this all documented. Get the letters he is sending and KEEP them in a file. Call the police and lodge a complaint about the phone call. Just tell them you are being harassed and that you would like a record of this phone call just in case the problem escalates. I think they would be in support of that idea. You don't have to take action just yet, but if I were you, I would definitely get prepared. Document EVERYTHING you can on what this guy is doing to you. Be careful not to say anything bad about him, too, because it sounds like he is devious enough to dig up anything he can on you. Remain professional as you can, but keep a record of everything he does. And by all means, if you begin to feel unsafe, contact law enforcement immediately!

Best of luck to you!
Angela