Have this ever happened to you?

I booked a three-day stay at a Marriott on Long Island and on the day of arrival, before cut out time 18:00, canceled it. Got a cancellation number and thought everything was fine.

Some days later I got a “Thank you for staying” email with a folio of three days with a charge of about $500. The stay also shows up under my Account Activity as well as on my credit card.

I just replied back to the email found in the efolio email with the Elite Member email on CC. So far, no replies. But is this a glitch or is this scary? Could they have checked in another person on my canceled reservation and had this person charge my card?