If you ever do this offer the site makes it very difficult to cancel your membership. Very easy to upgrade, which is nice though.
Call this number, give them the email address and last four numbers of the credit card used to sign up for emusic.

Call 866-240-9271

Oh and by the way, if you plan on keeping emusic, call this number and act like you are disinterested and they will offer you more music free (five dollars worth), at least use this you may become more interested in staying.