Cease and desist letter

I would like to write a C & D letter to a 3rd party collection company that is harassing me. They are calling for someone with my name but it is not me. I see samples but they include acct# which I don't have because it is not me. And include dealing with the company directly but again, it's not me and not my debt. Is there a sample letter for contacting the incorrect person? Thanks for your help