You should have received $100 cash - if Platinum, $100 + 2 free nights. See below:
The Ultimate Reservation Guarantee: To be eligible, your Marriott Rewards membership number and a valid credit card number must be part of your reservation. If unable to honor reservation, the hotel will pay for your accommodations that night at a nearby comparable hotel and compensate the member for the inconvenience. Compensation varies by lodging brand (see below):
* At Marriott Hotels & Resorts; Renaissance Hotels & Resorts; Marriott Conference Centers; Marriott Vacation Club International; and Horizons by Marriott Vacation Club: Alternative accommodations, plus $200 and 2 free room certificates.
* At Courtyard by Marriott; Fairfield Inn by Marriott, SpringHill Suites by Marriott; Residence Inn by Marriott; and TownePlace Suites by Marriott: Alternative accommodations, plus $100. (Platinum members also receive 2 free room certificates.)