So, based on what the support system says, you have gone down the punishment ladder, which means after your 14 day temp ban, Riot deemed you worthy of downgrading your escalation status.
https://support.riotgames.com/hc/en-us/articles/207489286-Instant-Feedback-System-FAQ-#h1q3
HOWEVER, based on punishment escalation systems this is the order:
10 Game Chat Restrict
25 Game Chat Restrict
14 Day Temp Ban
Permaban
In theory, you are two infractions away from a permanent ban, however, it might be possible to get escalated further if you have a history of punishments. I recall seeing some posts where there were repeat offenders who would go from chat restrictions to 14 day temp bans, then go back down to chat restrictions and then go back up to temp bans and keep yoyo-ing back and forth and Riot just slaps them with a permanent ban because they keep repeating the same kind of behavior over and over again and Tantram comes into the thread and is like "this is your 9th punishment. Permaban was rightfully issued. This will not be reversed."
So, the safest bet is that you should really try to follow the guidelines of chat... ie if it's not for the purposes of creating teamwork and cooperation, then don't type it. Riot has said many times that the primary purpose of chat is to help facilitate cooperation and create teamwork. Don't clog it with arguing with teammates, don't be negative, don't harass people, don't flame people, etc...