Maintenance for the week of March 24:
• PC/Mac: NA and EU megaservers for patch maintenance – March 24, 4:00AM EDT (8:00 UTC) - 10:00AM EDT (14:00 UTC)
• Xbox: NA and EU megaservers for patch maintenance – March 26, 6:00AM EDT (10:00 UTC) - 12:00PM EDT (16:00 UTC)
• Playstation®: NA and EU megaservers for patch maintenance – March 26, 6:00AM EDT (10:00 UTC) - 12:00PM EDT (16:00 UTC)
Were you over level 10 before the Dragon Bone update? You'll unlock the horse when you get another character up to level 10.
(since it's a collection unlock, you'll be able to use the horse on all your characters once unlocked once.)
Or do a quick level to 10 on a new toon. Should unlock for you, also if you hit 10 since the patch it should be in your collectibles if you missed the notice.