I got a message from the American Express today as following. Apparently the hotel does not have proof that I ever authorized the charge.

"We would like to advise you of the status of your inquiry on your account from SPRINGHILL SUITES. We are pleased to let you know the inquiry has been resolved in your favor because the merchant has not yet provided the necessary information. Therefore, we have issued credit to your account for $xx.xx which will reflect on an upcoming statement."