When a merchant has refunded money to your debit card it can take from 5 to 7 days to see the money returned to your bank account.
However sometimes you may get the refund returned to your bank account within 24 to 48 hours for some banks depending on how fast they process the transactions.
But you should receive the refund on your debit card within 7 days and if you haven't you should speak to your bank and the merchant to make sure the merchant refunded you.