Heya friend! If you would kindly post the logs, I could look at them and see what could have possibly triggered your chat ban. Usually, the bans are handled in a 4 way tier.
- First offense: 10 game chat restriction
- Second offense: 25 game chat restriction
- Third offense: 2 week ban
- Fourth offense: Permanent ban
These tiers can be jumped depending on severity of situation
Because you're either the first or second tier, it COULD be a false alarm, but the Instant Feedback System is pretty well developed and doesn't false ban/punish people as much as the community thinks. Just make sure you're positive, and don't say things that you regret, and you'll be fine! Logs would be great to help you figure out why the Instant Feedback System was triggered.
Source of tier punishments: http://boards.na.leagueoflegends.com/en/c/gameplay-balance/Boqd81O0