On Serebii it says to put 1 pokemon in each box, then leave the PC and come back. But I have like 28 in each of the 16 boxes, but I still don't have 24 boxes.
What Serrebii told you is true. Make sure you completely leave the PC. Check and Make sure you have one in every box.(You might have overlooked a box).If it still doesnt work your game is glitched.