The WordPress plugin doesn't work.
A few things can prevent the Wordpress plugin to work smoothly:
If you use a cache system like W3 Total Cache, don't forget to add /feed/ in the plugin exception list.
Check that there's no other active plugin like FeedBurner that tries to also redirect /feed/.
If your redirection is still not working, try to delete and add the plugin again.
Finally, don't hesitate to contact us if you still have issues.