For online orders, Apple usually only charge your Credit Card just before the iPad ships to you - at which point it is usually too-late to cancel the order fulfilment. As such, if you were able to successfully cancel the online order, no charge is likely to have been made - and therefore no refund will be due.
If you have any concerns, check with your Credit Card issuer - as they will be able to confirm whether or not a charge has been made to your account. Be aware that when placing your order online, a "hold" (but not a "charge") may have been made. The "hold" merely checks that you have sufficient credit - and temporarily holds that credit until the charge is made. The hold will expire if the charge isn't subsequently made by the retailer.