My device was received in Fort Worth on December 19 so about two months.  I did have my tracking number but that didn't seem to help my cause.  I called Customer Service several times myself.  I had my local wireless store (We R Wireless) call on my behalf twice.  And yesterday I called from the Verizon store.  Each time, I was assured that I'd be receiving a credit in two to three business days -- except for yesterday when they said it could take another month.

FYI.  I believe my issue came about because the 5S I returned was a replacement from the Apple Store.  Shortly after I bought my iPhone 5S, a chip overheated and destroyed the phone.  I think the warehouse was looking for a phone with that serial number but what I returned was a refurbished replacement phone.