You have quite a good deal of legislation from which to select, I believe you may be best served by The consumer Protection (distance selling) regulation 2000. You have not had the opportunity to inspect the goods and the order was placed on line so the DSR 2000 applies and the goods have now have been sent to the incorrect address, under the above act you have 7 working days in which to cancel the contract from the day after you receive the goods, which you have not yet done, but you must cancel in writing or other permanent form. The supplier should then make a refund of the full amount paid including any delivery charge, which they will if the situation is as straightforward as you say.