You'd best call again I think. There are others who work there so you might have better luck. I'm only saying because the question is too vague to get a definitive answer as to why you've lost it.
I'm in asimilar boat in that I've recently moved. I stayed with BT but had to have a new email address for some reason, and I can receive mails on the old account but have been told at some point I won't. It's annoying me because when I try to solve it they say "go here and do this" and it just doesn't work. I'm still with BT so why can't I have my old address too?