Anyone can sue anybody for anything at any time. However, just because they say they will doesn't mean that it will happen. People say all sorts of things all the time. Sometimes people change their minds. Sometimes people lie.
Your best bet is to tell them to quit calling you and you'll deal with their legal action when you receive it. If you actually get sued, retain a lawyer.
You can reach Harkess & Salter LLC at (303) 531-5380 or info@Harkess-Salter.com. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.