To help get the property's attention, you might think about contacting AMEX and challenge the charge telling them exactly what happened. Also, contact VISA and ask if they can see the swipe of the card at checkin. If so, you then have proof the property has messed up (not that your word should be questioned). And finally contact Marriott Customer Care (not Marriott Rewards) and explain the situation and ask them to contact the property for your desired resolution.

A credit and recharge sounds real simple, but I find front desk people will tell you whatever they can to move you along. I was standing in a room with two queen beds and the FD clerk was telling me that room was a king.

Good luck getting this resolved.