Sadly if riot determines it is justified then it is.
for those wondering why then you can start with the terms of use page
https://na.leagueoflegends.com/en/legal/termsofuse
where section 5 (code of conduct) article 5 states
"v. Transmitting or communicating any content which, in the sole and exclusive discretion of Riot Games, is deemed offensive, including language that is unlawful, harmful, threatening, abusive, harassing, defamatory, vulgar, obscene, sexually explicit, or racially, ethically, or otherwise objectionable;"
So end of story is that you and the rest of use agreed (or bypassed the agreement and should be banned anyways), as such banning you is within there right as you agreed.
And no I do not believe ignorance due to not reading something before clicking agree is reason enough to be released of such agreement