NCOS credit collections unintelligent and refuses to tell me who and what is owed/calling everyday horsham, Pennsylvania

Morons call me everyday.  When I get called, I call them back.  Karen Anderson called me to tell me to stop calling them! I am going to send a letter to the main office and request that this be stopped.  I wil send it registered.  I was called and told to stop playing with the phone and that I was too old to do this?  Karen Anderson's phone is unknown and cannot be called because a msg. comes up "failed"?  I have no idea who I owe, so this is a scam to frighten a person to send in a check. If they are still using these tactics, getting a lawyer does no good!