It depends on your debit card issuer. Visa and Mastercard both now allow you to reverse debit card transactions; however, banks are very poor about honouring them so you may have to push hard and quite possibly make a complaint to get anything done. Keep at it.

Also, put in a claim for the value of the voucher against HMV (find the administrators website and follow links for unsecured creditors). Takes a while but you should get something back eventually.