What you could do to help the C&A mods here, is that you look at the history of those two players.
How many games did they play together ?
what's the win rate of each of them in the games they played together.
If they played 100 multiplayer games together, and at least one of them won like 90% of the case, then there is definitely something fishy going there.
If they played 100 3-player games, and like player A won 40%, player B won 30%, then that's close to the expected 33% and you have no case.
Furthermore you can check a few of their finished game together, check the log yourself, and show that clearly they were helping each other.
If you want example that's how I report people for SD (2nd one is more elaborated, going through logs of few games) :viewtopic.php?f=239&t=238441&p=5258775#p5258775viewtopic.php?f=239&t=227522&p=5033005#p5033005