Each player's merit is measured based solely on their own behavior. Context does not matter in Riot's reform system.
If you did anything worthy of a 14-day ban, it will give you a 14-day ban, even if other people were harassing you the whole time.
Those people will probably be punished too, since telling someone to kill themselves is extremely wrong and hurtful, and Riot does not tolerate such implications.
Here are a list of things that I know of that can result in a 14-day ban:
- using zero tolerance phrases, even when quoting others. This includes hate speech, bigotry, and telling others to kill/harm themselves.
- Intentionally feeding
- behaving negatively without showing significant reform after having already received a 25 game chat restriction
I suggest you look at the ToS and summoner's code to get a better idea of what your responsibilities are with regards to controlling your own behavior.
My personal best suggestions for you are to mute players when you see that they are harassing you. You can report the player after the game. And you need not argue with them. Doing so will either feed them attention (if they are trolling you for a reaction) or anger them further (if they are just tilted and angry with you). So it is almost always better to mute a player and report them after the game instead of wasting time engaging with someone you know has no intention of listening or being nice to you.
Never fear threats or calls for reports, because the system throws out false reports, so if you did nothing wrong then you won't be punished. Additionally, there is no such thing as 'ganging up' with reports. Multiple reports do not stack, so again - you need not fear somebody calling for others to report you.
Lastly, remember not to stoop to another player's level. If they are doing wrong then you can report them knowing it will catch up with them eventually. Taking justice into your own hands or trying to hold them responsible for 'wronging' you will never end well for you. If you cross any lines while doing it then you will just get yourself banned like what happened here.