Call the hotel and ask to speak to accounting or a manager. Don't ask a desk agent to do the reversal - often they aren't trained on how to do this. When I worked for Marriott (as an assistant manager) only 1 of my desk agents was trained on how to do a reversal of a card charge. It was easier for me to do it myself and know it was done properly. I would try the property before I'd go through Customer Care etc.