Hi -- Did you pay for this in the shop ? if not........
Under the "distance selling regulations" you have a Seven day cooling off period that gives you the right to cancel an order that has been made for goods that have been purchased at a distance i.e...... over the phone, internet or where there has been no face to face contact.
Simply contact the trader if applicable.. stating you are exercising your legal right under the DSR and you request their agreement that an immediate refund will be made back to your credit card in accordance with the DSR legislation. To cover your own back send a letter to confirm what you have requested, just in case it's disputed as you will be able to use that to enforce a possible future charge-back claim through your card in case they don't comply.
If not then phone them and state you would just like to cancel, you never know.