Did you read the fine prints about the "FREE" cancellation? There is always one.
A very popular clause will be, you must cancel up to a day before the reserved date. They have this in almost everything I booked anywhere. Some are 3 days before, etc...
Just check priceline and their "No cancellation fee" applies to up to 1 day before the reserve date. Otherwise, they could charge you up to a full day.
If you cancel outside of that 24 hours requirement, I would dispute it with their management or customer service. call them up.
Weekday Commuter...
Weekend Commuter!!!