I have this happen, not with Hyatt yet but it can happen. I booked a hotel room at the City INN London with a rate with a 24hr cancel policy. I canceled and was charged. I called and the hotel informed me that the rate I booked was advance booking. They would not reverse. Fortunately I kept my e-mail booking with cancellation info. E-mailed it and still no reverse. Finally credit card did reverse. It is best to create a folder for hotel reservations and a hotel cancellation folder just in case. I do them by quarter and year. Also, this is good if you a folio and need to have the hotel create one for expenses.