I know exactly how you feel and sometimes it's legitimately not your fault. It only takes several unlucky games to ruin your MMR and then you are given impossible games.
I'm telling you this as a high elo player. I'm low Diamond in NA but I almost hit masters in KR last season. Add me if you want, I can give you some encouragement/tips.
Sadly, high elo degenerates with their disgustingly deluded egos will tell you it's always your fault. So are a lot of people in boards who downvote posts like these.
I'm not even joking, try and post a game where you go 15/3 and the rest of your team combined is like 8/48.
These people who duo qued to plat or diamond that aren't even half as good as they say they are will look at that game, ignore how every other lane was giga feeding and tell you to buy a blue trinket ward- even if the rest of your team isn't fking warding.
I've seen so many unlucky people like you who are undeservedly stuck because of bad teammates and ruined MMR.