Why was I placed with a toxic player in a following game after reporting them?

So, I'm in my promos, my mid laner is flaming hard and I keep my cool throughout the game, I report them for toxic behaviour and yet the very next game I begin, the toxic player was in my team once again. I did mute the player but it did have an effect on everyone's gameplay. It's really unfair, I cannot dodge because it is my promos, and I have to stick with this toxic kid for another 30 minutes. (lost that game also, thanks).