Acrobat Professional (Perpetual) - suddenly signed out and disabled

I have a perpetual version of Acrobat Pro (purchased in 2015). A couple of weeks ago I opened a PDF and was informed that I have been signed out of my account and the majority of features had been disabled. Whenever I click on 'sign in' in the top right hand corner, nothing happens. If I click on 'Help' then 'Sign Out' a box appears telling me that I am not connected to the internet (when I am). 

I have been informed that Adobe no longer support perpetual products via chat or telephone and was recommended to reach out via this forum.

Any help would be hugely appreciated.