I cannot erase authorisation due to my email account no longer existing

Hi,

I have just purchased a very expensive ebook for university and when I try and download it I get the following error message: E_ACT_NOT_READY

I think (not sure) that this is because my adobe digital additions app on my Mac is currently authorised with an old account. I cannot erase authorisation as I do not know the password for that account and the email address no longer exists (it was from a previous education institution.)

I purchased the ebook on my new adobe account which is associated with my current email but I cannot figure out how to add a new authorisation without erasing my previous authorisation (which I cannot do).

What do I need to do to fix this?