The payment method he asked for was World Remit, which was new to me. Register and then use your Visa/Mastercard to send money. The seller said the transaction with World Remit would be complete in 1 hour.
In this case, contact WorldRemit as soon as possible and ask to try cancel a transaction :
How do I cancel a transaction that I have made?
If you wish to cancel a transaction you have made, please contact WorldRemit as soon as possible. After a transaction is paid out we may not be able to refund it, so it is important you contact us as soon as possible to minimise this possibility.
Or even better contact your bank and explain what happened, I believe they can get the money back. This is not a BTC transaction, which in most cases is irreversible; the whole thing works differently when you use banks/cards.