When I tried logging in to my old account, I ended up creating a new dummy account under what I believe is the same name. When I went to try to recover my old password, neither of the 2 emails I use were registered.
How do I log into my actual account and get my forum back up and running?
My best guess is that, through a lack of activity, your forum has been deleted. You will have been sent an email about pending deletion several days before this happened but, unfortunately, mail services with over agressive spam traps can treat such mail as spam and they are easily missed by forum administrators.
There is no such thing as "an account with Nabble". You register at each forum you use and those registrations are as different as the accounts you may have with Amazon, eBay or your ISP. Why would you expect to register at eBay and be able to login with the same details at Amazon - unless you had also registered at Amazon with the same details.
Just a Volunteer Nabble Helper - because the nice folk at Nabble have helped me!