That is most definitely a phishing e-mail. If you put your log-in or any personal information into any forms that the e-mail may have linked you to, please submit a ticket to our support site (linked below) and ask for an account name change. Select “Account Issue” from the drop-down menu for this particular case. You’ll need to supply us with an e-mail address that has never been associated with your Guild Wars 2 account before as well.
Additionally, ensure that the password to your e-mail account is not the same as the password to your Guild Wars 2 account; individuals who send these types of e-mails usually attempt to log in to the e-mail account first with the information that players provide to steal it in an attempt to better gain control over an account.