send a registered letter, something your neighboor has to sign to recieve. gives you a paper trail. if you are 100% sure this is your property, wait an appropriate time 2-3 weeks after sending the letter, then, send another one. this may seem like a pain in the butt, however it shows a real attempt by you to contact this person and like i said a paper trail. if you still get no response, go ahead with getting it out and send the bill to your nieghboor. also getting a survey done to prove the property line would be beneficial. you will most likely be able to sue the person for any out of pocket expense if these criteria are met