I work for a reseller who provided a student with a copy of Design & Web Premium (before Creative Cloud was available) before he took a gap year from his studies. Since returning, he has gone to install the software and input the serial number, only to realise it was actually Production Premium he needed.
We have purchased him a copy of Creative Cloud, so he now has the software he needs, but he has been kind enough to offer to return the unused copy of Design & Web Premium. He tried contacting you himself to get the serial key de-registered, but was told the reseller would have to contact you directly. Reading the chat transcript, included below, it looks like the software cannot be de-registered, but we may be able to get a new serial key for it? Please could someone contact me about this or provide me with an email address where I can send the serial key etc and discuss in more detail?