Need help activating CS5 Extended

Hello,

I have CS5 Extended as an upgrade edition.  When I install it on my new Win10 PC, it installs fine and I am able to enter my CS5 serial number.  The serial number is accepted but it then says a qualifying product was not found.  I then select CS3 from the drop-down menu and I enter my CS3 key.  Unfortunately, the installer then says my CS3 key is not valid and I'm stuck at this point.

When I did this in the past on a new PC, I worked with Adobe support and they had me hold Ctrl-Shift while double-clicking the serial number dialog box.  When I do that now, I get a new box titled "Enter Serial Number Upgrade".  I am presented with a Challenge Code that I am supposed to give to an agent and then the agent is supposed to give me a Support Code in return.  I just had a chat session with an Adobe agent but unfortunately, the agent informed me that s/he was unable to provide me with a Support Code because CS5 is an old product.

I understand that Adobe has moved toward offering cloud-based products but in my case, this CS5 product does what I need it to do and it is still supported on the Win10 OS.  There must be some way to generate the code that I need to complete my installation.

Thank you for reading!