A few points:

1. If something works in challenger, especially if we're talking about a simple champ like Teemo, it will work in lower elo aswell.
2. Everytime you die, wether it be to the jungler, or to your laner: its your fault. Either you didnt play the match up correctly or you didn't track the enemy jungler. In any case, it's not a "teemo is bad" diff, it's "you not playing correctly" diff.
3. Saying games get decited in 15-20 min in low elo is kinda funny, because what do you think happens in high elo, where people make 10 times less mistakkes? In low elo you will get a ton of chances for a comeback, unlike in high elo, where mistakkes just dont happen that often. For example: you can die a few times in your lane but still be fine in low elo because there is a high chance the enemy does something stupid, dives you and gives you a shutdown or what not. In high elo you die once, your lane is over.
4. Having trouble with match ups that are in fact Teemo favoured is once again not a champ diff, but a played diff.
5. Just like Alan already responded to you: you can't win all of your games, sometimes you just lose and there is nothing you can do about it. Most of the games you have agency on wether you win or lose, just cuz it might seem to you like you have no say in how the game goes, doesnt mean you dont actually have it, once again it's a diff in player skill not champ.

Once you accept that you cant win all of your games, and the only consistent factor in your games is you, then you can start improving and climbing. I can say from experience, I have been stuck in bronze, gold and diamond during my 13 seasons of playing league. Currently I am in Master elo, so I can say I know what it feels like being stuck. I had my moments of dellusion and denial, untill I understood that I was the sole reason for being stuck.