@ Luis Vlad - This thread is for reporting forum related issues and is not for in-game issues. It is manned by the Forum Moderator team, who are all players, like yourself, and are unable to see details of other players' accounts.
If you think it was a bug, I suggest that you submit a bug report about your cape.
How to report a Bug
If you had the cape when you logged out and it was missing when you logged in, it's possible someone else accessed your account. In which case, you should follow the instructions to secure your account.
Securing your account