Wrongly banned for "Repeat Offenses"

The “repeat offences” part of that message is standard text, and appears in every ban notification, even if a player has cheated once and only once. 

Cheating isn’t just about GAC (though I did find one suspicious battle where you had defeated a Chimaera fleet containing Hound’s Tooth and the Hound’s Tooth still had protection). Players can cheat in the raid or during unlock events as well. 

There is always a remote possibility that one of your recent GAC opponents where you bothered to try may have been disgruntled and hit the “report” button in game, which led to a dev not properly checking your history and banning you. Hopefully an appeal is successful in that case.