Serial Key for a CS6 reinstall on a new computer won't work

I have Creative Suite 6 (Design & Web Premium) installed on my very old desktop computer (Windows 7) and also on my backup laptop, as permitted. I just bought a new desktop computer, and deactivated the license on the old desktop computer so that I could install CS6 on my new desktop computer (Windows 10) instead. I have the original CS6 package with the physical disk and the original serial key, but when I tried to install, I'm getting an error message that "The serial number you entered has been revoked." What's going on? Why should it be revoked? (I read other posts about activation problems but none are duplicates of my problem). My CS6 is original software and not a pirated copy. The software was duly purchased, and is now only active on my laptop. My old desktop computer is being deactivated and decommissioned. CS6 is perfectly fine for my purposes; I have no need and no desire for Creative Cloud and its subscription model, nor storing any files in the Cloud. All I want to do is install my CS6 on my new desktop computer as originally advertised. It's my understanding that CS6 will work fine on a Windows 10 machine.