I feel as though I am being "stalked" by someone from outside my family. It seems as though they know my every move. Do I have any legal rights?

They know when I travel, where I go and even who I talk to on the phone (cell). I just recently found out they did a back ground check on me through backgroundchecks.com . This person is currently married to my sister, but in the process of a heated divorce in which I am currently giving her moral support. I''m not sure why he is doing this but I would like it to stop. What are my legal rights?