Cannot ride my horse! already learned

Dear players

I already paid my riding skill fee, but cannot find the skill icon in my skill book.
I can neither use the horse directly. It keeps saying I do not have the riding skill.
Any one can help?

MageID : Oucl

Are you sure you bought this skill? Horse Riding - Skill - Classic World of Warcraft
Make sure to delete your WTF WTD folders while your game is closed too.