I have been a Marriott Rewards member for over 20 years. During that time, I have probably made thousands of reservations via the Marriott website.
Whenever I make a reservation, I do three things:

• Write down the reservation # or print out the confirmation page
• verify that the reservation shows up in my account
• verify that I receive the confirmation e-mail (which is almost always instantaneous)

Seems like you failed to do any due diligence. Based on the facts, I'm guessing you did something wrong.
But as usual, people here like to play the victim card and blame Marriott for their failure to take even the most minimal actions to secure a reservation (if indeed you did make a reservation).

Marriott owes you NOTHING.

Newman