Has called several times. No message left on my answer machine.

Hang-ups or "This call is for Ann Jones" and then dead air.  If you call back the number, they say it's American Express but can't look up your account.  Amex hired this outside company to follow up on late payments, etc.  But now they are calling a day or two before statements are due.  Call Amex directly to see why they have you on this list.

same here today, they called 4 times today, they claim to be american express, they won't sent statements then harass us when they don't get their money

if they can't send statements, how can they expect payment? I'm not sending one cent until I see a statement

Called my cell phone 2 times this morning.  Answered it and a woman finally spoke up and asked for "Susan Nitzle" (not sure about the last name) Then she asked "Do you know her" and finally said "okay" and hung up.  

The time lag after answering and background noise was similar to someone calling from a phonebank or call center.  I believe that the cell phone number is "spoofed" and that this call was scam.  Probably pretending to work for a credit agency or AMEX.