What can I do about ex landlords calling my place of employment every day?

I moved out of the house I was renting with my wife when we seperated. Our lease expired in August, so we were month to month. We gave 30 days notice and I cleaned the home and there was no damage what so ever. They have been harrasing me daily, calling my place of employment and telling anyone that will listen that I am a thief and liar and should be fired from my job. They are demanding that I pay them rent until the summer when they can re rent the property and will not stop calling until I do so! Can I get the police involved? What are my rights, can I go after them for slander?