Trip Was Cancelled-cant Cancel Priceline Rental Car

My trip was scheduled for Sept 10-12  Now cancelled - I do not need the van I rented thru Price line - It was an upgrade to a mini-van- On my email from Itinerary Air@ trans.priceline.com - It does not state that I could not cancel or change. There was a place on their web site that I read that you could cancel or change- Shop & Compare Prices Search for our best available published rental car rates from the rental company of your choice. Choose the price you want to pay. Reserve your rental car through Priceline. You are not charged by the rental car company until you make the trip. Rental car reservation can be cancelled or changed at any time. So does anyone have any suggestions to stop them from charging my credit card....