Issue authorising a book in Digital Editions on a new laptop

I purchased a book some months ago and activated it on the laptop I owned back then. I need to read this book on a new laptop but am unable to access it.

Steps I've taken: 

• I've de-authorised DE on my old laptop as per the steps here.
• Now when I open DE and attempt to open the book on my new laptop, I'm told by DE "Authorization Needed".
• The eBook vendor is set as Adobe ID.
• My standard Adobe ID & password do not work and I'm really struggling to figure out how to access this eBook that I paid for. 
• It seems I cannot reset the password in a standard password reset manner either [ie. click reset password and an email is sent to the email in question with a new temp. password]
• Adobe chat were unable to help and directed me to here!
• Pls see screenshot of what I see in DE

Please help!

Thanks!