You didn't warn them properly. For the next time say something like this: [name] and [name] teaming is not allowed 1/2 And then if they don't listen to you, warn them for second time with the same message but... 2/2
I always warn players with 2 or 3 warnings. Why? Because this is a better way to warn and it makes easier Mods to punish them.
A perfect warning would be: Player1 and Player2 Teaming is not allowed. Please split up Saying something like 'stop teaming' or 'split up' doesn't really tell them that teaming is forbidden.
And then if they don't listen to you, warn them for second time with the same message but... 2/2