my hallowween costume disappeared
You will need to contact support following the support link at the top of the page and then the submit a request link on the top right.
Have you tried speaking to the Black Lion Trader (Armorsmith) in the city of your choice, to pick up your Outfits/Costumes that were affected by the implementation of the Wardrobe? You may find your Costume there, or in your bank or a character’s inventory.
Good luck.
You bought it but did you ever double click on it to add it to your wardrobe. If not it may still be sitting in your bank or on the character that got the mail
If your mail is full, e.g. more than 10 messages, you won’t receive your order by mail from a.net until you delete at least one message.
Once you receive the mail, accept the item, double click it. It will be unlocked account-wide.