You can cancel the order with them and if they do try to charge you, do a stop payment. Show your initial receipt to your bank when you are doing the stop payment (if they try and charge you again) so that way you have proof of when you ordered. Was there an anticipated delivery or ship date on when you ordered? That's why I hate Horseloverz.com. They takes AGES to ship.
Also, according to the FTC and USPS, if you cancel an order and they send it anyways, it's considered a gift and yours to keep. Just make sure you watch the postmark. If it's marked the same day you cancel, don't open it and mark return to sender along with "order cancelled on 12/XX/10.
Hope this helps!
*Dreams are within reach, you just have to go that extra mile to catch them*