I finally was able to chat this morning, and apparently I got the right agent. He reset everything, and now Overdrive works again! He said you get six activations per account. Four left! I will be more wary of updating in the future, I probably should not have uninstalled/reinstalled Overdrive as they told me, because that's what invalidated the authorization. Anyway, I just wanted to let you know it's working.
Thanks so much for your help.
Filomena