Hi, i bought a full demon (yes with hair) more than 24 hours ago, and i'm not getting the achievement, what happened?

If you checked the achievement, it says
Which is basically 2 full sets.

This could possibly be a glitch, or just faulty coding.

There has been an issue with achievements for a while now, most achievements do not appear as some do. You can possibly contact an admin to handle this situation. Also the above post may have some relation to your issue.

Also, since they're updated every 24 hours, perhaps you bought it right after the update an thus making your wait about... 23 more hours.