Got banned for repeating a word that my teammate called me

I know that saying homophobic, racial slurs is against the game. But in this instance I did no use it against anyone. My Lee Sin called me the N-word and we got into a small argument over my kda because I was feeding(not intentionally). As the game was coming to an end I said in all chat to report Lee sin for calling me the N-word. Instead of saying "N-word", i wrote out the word, "%%%%%%." It was a big mistake on my part and resulted in me getting banned... I just think the punishment was a bit too harsh but I do admit I shouldn't have wrote the word out even if it wasn't used against anyone.