upable to download book from site to ade because item is bound to a providers account and I need a unlock code and username

I bought a book from a book site (BN). tried to download to computer and get error message:a this computer is not allowed to open 9781420132663_epub.v2.epub because this item is bound to a provider account.  To open on computer enter account username and unlock code associated with the item.  what do i do