The seller can't accept a different address after the sale.
They could cancel the label they have bought and simply write the address they currently have onto your parcel and then pay to send it from the Post Office.
Or, the seller could cancel the sale so you can buy the item again in a new transaction, adding a different posting address at checkout.
Depending on how you paid, your payment might take a while to be returned to you.
Paypal is more or less instant. If you paid with a credit card, it can take a while to appear on your statement.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)