Ive been playing for like 6 to 5 hours on flood total since castle map pack came out and i havnt seen any of the new maps… Wtf and in playlists its says theres 2 of the castle maps in there wth i payed to play on new maps and i cant even use them… And they seriously need to reduce the knife lunge on this piece of crap game that has the same problems since realise date, and nothings been fixed! Expect for some little twerks, and they say 343 is trying theyre hardest LOOOOOOOOOL my poo could build a more complex and fun non rageing game xD i miss bungie so much 
!!! But anyways can someone explain why aint I getting to play maps i paid money for!
Try to play with friends who also have the Castle map pack.
It increases your chances of the Matchmaking system pairing you with players who also have the Castle DLC, thus increasing the chances of being able to play Flood on those maps you desire.
Wait so if im in a flood lobby and everyone has the dlc except for one person, none of us can play it??
> Wait so if im in a flood lobby and everyone has the dlc except for one person, none of us can play it??
If that happened, I expect that none of you guys would be able to play it.
However, that is very unlikely to happen. If that many players in the lobby had the DLC, then the matching system would probably look for one more person with it.