This number was left on my parents message machine.  I haven't lived there for 15 years and they said it was for "debt collection".  Great.  Who the heck is it?

Didn't say their name, just left the phone number.

I received a call asking me to call this number back. I called them back but no one answered it just kept hanging up on me. According to the message left for me it was a collection agency named Carolyn Riddle law office is what the person leaving the message says.

CALLER LEAVES MESSAGE-CANT UNDERSTAND FROM WHAT COLLECTION AGENCY
KEEPS REPEATING MY NAME AND LEAVES A PHONE # TO CALL BACK - WHEN I CALL BACK IT RINGS TWO TIME THEN HANGS UP .

CALL CAME IN COULDN'T UNDERSTAND WHO IT WAS
WHEN I CALL BACK THE # THEY LEFT IT RINGS AND THEN HANGS UP.
I'VE TRIED SEVERAL TIMES AND GAVE UP

Could not understand name of firm or organization calling.  Message stated that it was a debt collector.  When I tried to call the number, several times there was a busy signal.  Tried again later and after ringing several times, a busy signal came on again.