You didn't call yourself gay, you called yourself a homophobic slur.
Look, I'm not gonna be dense and insinuate that you're homophobic or self-hating or anything like that. But your words are indistinguishable from somebody that IS spreading hate. You can try submitting a support ticket to explain the situation, but you'd probably be lumped in with actual homophobic jackasses claiming to be gay to try to avoid being punished for using slurs.
Surely, as a gay individual, you don't think you're going to have an effective conversation about the nature of treatment of homosexuals and the use of homophobic slurs as insults DURING a game of league, do you? Because that's not an appropriate use of chat anyway, even without the slur use.