I had the exact same issue.
I created a GW2 account (you don't need the game, just on the website) and contacted support, explaining that I no longer had access to the email I used to log into GW1 and couldn't remember the password.
So I provided as much information as possible: character names, whether they were PvE or PvP, which version I bought and how, and the expansions. Even my pet's name, which miniatures I remembered having, and specific skins—basically everything I could think of. The next day, they merged the GW1 account into the GW2 one, and now I'm able to log in.