Thank you, unfortunately the issue is indeed persisting. Here's how it currently stands:
So I uninstalled office completely from this PC then I followed the link and enter my Product Key and get this Screen:
I download the Setup.exe and run it and then it asks for my Product Key again but this time I get this message:
I can't press the "Continue" here but the installation does complete successfully and I can open office apps but at that point we're back to square one with the original message appearing when trying to activate.
Although according to my list of installed programs I have Office Professional Installed (not plus) but the message I get when trying to activate references Plus (I don't know if this important or a red herring):
I do have an original Setup.exe that I got when I first purchased this product and that one installs Plus but runs into the same issue when trying to activate.