I received another email on the 3rd of August (after I figured they'd just given up on me) apologising for the way my problem had been handled so far, and asking for my birthdate and (again!) my email addresses. I supplied the information.
This morning, I received another email asking if I had access to one of my gmail accounts still. I replied and said that I did.
This afternoon, finally, I got a link via that gmail address enabling me to reset my password and secret questions. They said that apparently I made an online purchase at some point on my Guild Wars account, which integrated my account into some NCSoft master account, and so the password reset option on the Guild Wars interface will no longer work for me and is why I never received any emails when I tried to reset my password from there (I assumed it was because I wasn't sure of my account name...)
So I logged in and it's all working! Glad they could fix it in the end.