Call the property directly and ask to speak to the General Manager. Kindly and graciously explain to him the problem and ask what he can do to rectify the situation.

I had a similar situation when I tried to cancel an internet reservation. When I called to cancel at 4 pm the day of, they said the reservation had been posted as a no-show because I wasn't there last night.

Apparently, I had put in the wrong date on the website when making the reservation.

The GM of the property was quite understanding and agreed to refund the charges.