I'm currently having a similar issue with a different site regarding a withdrawal to a Natwest account, this is what I got told,
"In regards to your user account, unfortunately your recent withdrawal request has been declined by your bank, the funds have been returned back to your account and re requested"
They then asked for,
• Name as it shows on your bank account
• Name of bank
• IBAN number
• BIC/Swift number.
Hopefully this isn't a long term issue!