Two Promo Loses One Game?

I was playing Ranked Flex, to get gold, and I was in my Promos to Bronze I from Bronze II. I had won 4 games in a row, and I was 1 out of 3 games of my flex, and I had won. Then I lose a game as Darius, and after the game it said my promos were unsuccesful, I had played one game, but it showed two x's and one check mark. This is unfair, and even though it isn't difficult to get out of it wastes my time and my effort, and of other players. I feel I have been cheated by the system. Bullshit.