Once a payment is authorized it can't be cancelled by the buyer. It was already initiated so you need to wait for it to process. This means you can't cancel the charge for a purchae.
You may be able to cancel the purchase with the seller. The seller would then have to refund the purchase price. It is also unlikely the merchant would refund until the payment shows completed.
I'm not clear what you really did as you couldn't cancel the PayPal payment.
If you requested cancellation of the sale with the merchant, the merchant would need to acknowldge that cancellation and NOT ship the item. The merchant will then need to initiate a refund.
You'll need to work that out with the merchant.
