I am getting blank calls from this number, today morning 6am i got call twice when I answer it no sound from other end

This number just called me and left a message.  When I listened to the message the beginning of it was a phone ringing (like I had called someone and was waiting for them to answer) then a recorded message from NCO financial started in.

call was a non number an invalid when I called back.

This number has called several times. When I pick up the phone the caller will not answer me.  I called this number back and the recording I get is "Please enter your complete PIN". Another recording, "Please enter your PIN to access your voice mail."  It appears to be an invasion privacy. These calls come to my LAN line, not a cell phone.