If you submit a help ticket in game a GM will be able to unlock it for you.
I've had bugged achievements unlocked by ZOS before for me. As for the bug report if you can report some more information and they might be able to track down the issue and stop others having it.
@Turelus - EU PC Megaserver "Don't count on others for help. In the end each of us is in this alone. The survivors are those who know how to look out for themselves."
Note that in game you generally have an easier time submitting tickets about issues, as the web interface requires that you go through a filtering process before you can submit a ticket. Try right clicking on the achievement and see if there is a "get help" option as this sometimes lets you file tickets.
For the online ticket click "Web Assist" on the support site and the log in (this will link tickets to your account and give you more options) then follow the options, however it's very hard finding a category that will let you fill out information and is relevant to the issue.
@Turelus - EU PC Megaserver "Don't count on others for help. In the end each of us is in this alone. The survivors are those who know how to look out for themselves."