Permabans are the result of either extreme behavior (not just telling someone they suck) or through consistent negative behavior and working past multiple lesser punishments before that. If you already had a 14 day ban, then this permaban was the next step if you continued showing negative behavior to be punished again.
We all understand the frustration of a teammate not performing well, or even intentionally throwing the fight, but adding your own negativity to the situation never fixes the problem; more often it just makes it worse. Try speaking to them politely, and if they don't want to hear you out then just don't talk to them again. If they are being toxic in chat you can just mute and report them.
Being sportsmanlike to your team rather than fostering a negative environment lends to more productive teamwork and a greater chance at winning, along with being able to enjoy the match more. I suggest reading these articles for guidelines on being a more sportsmanlike player;
The Summoner's Code
Behavior Worthy of a Champion
If you want to discuss your punishment with the community I'd suggest posting your reform card. If you need to contest your punishment with Riot you'll need to submit a Support Ticket.