u/Apbunity

Bought the neith saga, and got a skin after i completed a game when i reached 11 as seen in the picture - i assumed the chest automatically gave me the reward skin after the match.

However, i completed a game and got 12/12, and got no reward? Which makes me think that i never really opened any chests to begin with?
Does anyone know how i can open and claim these champion chests?