Licensing issue

Since the virtual assistant was no help and there are no options to escalate me to a real person to assist me, I guess this is my last resort.

I had Acrobat Pro XI on my old PC.  When I tried to deactivate it before installing on my new PC, the deactivate option was grayed out.  I logged into my Adobe account and downloaded Acrobat XI from my products.  When it gets installed and I try to launch, I get error : 'Serial number already in use' [P.I removed by moderator]

I found a thread in here from 2017, but it references creative cloud, which I don't have installed, and all of the links in the thread are no longer valid.  I purchased Photoshop Elements (subscription, don't get me started!) and installed it when I got my new PC.  Don't tell me I need to uninstall it and do all sorts of crazy stuff to make my Acrobat XI work...