Please call them. Don't e-mail.
I have had nothing except copy/paste responses from e-mail...
They have trouble transferring my number over, but every email (for a fortnight) said they were experiencing technical difficulties etc..
Rang up, asked to speak to supervisor. He couldn't believe the problem, refunded the cost of the phone, gave me a freee months line rental and 5mb gprs for 6 months.....
Just ring and say you've forgotten it. You'll probably have to confirm ALL your details however...