You can't report it because there isn't any rule of nordeus saying that we must use a legal formation in all our games.
The only thing TE could do (and did), was to remove a heavy penalty for "illegal" formations.
It's a game, it's not the Top Eleven Football Federation - lol
Probably they are friends or for some reason he decided to support him.
Just try not to depend from other opponents results and if you have any of them as friend (or maybe someone else common friend) remove them because maybe you 'll gonna play in another season together with them.