Well I ran into a cheater and got the evidence. There is no way to report someone ingame at the moment so I'll just do it here.
Okay I wanted to show the video but this site won't let me upload more than 10048 kB
But you guys can check out the replay: ffb7306b-dc14-4cc8-8e1a-882ae129ba82
You start noticing the cheat near the end of the game.
The name of the player is Carry and his Steam ID is 76561198931049344.