Since the maps show up on private match, this would mean that they are working fine. The most likely cause of this issue is due to the matchmaking process. Since map availability is a factor for matchmaking, it may be most likely that the servers were trying their best to find you a match compatibility and there are chances that some of the players you are being paired with don't have the Devastation map packs and that is why maybe perhaps it seldom appears. I would recommend you check on your select maps or try other game modes. Hope this helps. Cheers!
Hi MiRaCLeS ,
Indeed, if you're able to see these maps in private then your download and install was successful to your account and console.
For further information on the how match making works, please check the information found in the link: http://support.activision.com/articles/en_US/FAQ/How-does-matchmaking-work-in-Pu blic-Match/?q=match+making&l=en_US&c=Game_Title%3AAll&fs=Search&pn=1