I got child support papers in the mail, that's not my child. what should I do?

That's not nearly enough information to even hazard a guess as to what is going on, or where it is going on. I suggest you start with the information and materials posted at: http://willicklawgroup.com/paternity/ http://willicklawgroup.com/child-support/ Then, if you are uncertain what to do or how to do it, you should schedule a consultation with a family law specialist.  if the case is not here, but elsewhere, you will want to contact an attorney in the jurisdiction where the underlying case is pending.