3 times this has happened. 3 times this matchmaking has punished me

This is the 3rd time since season 3 that I have had absolutely massive losing streaks after hitting a promo. This can't be an anomaly, this has to be something wrong with the match making system. It happened when I first got into gold 5 in season 3: reach the promo for gold 4, then lost ~20 games in a row to be dropped into silver 5 MMR. 4 months later when I managed to scrape into platinum, and then into the series for plat 4, I lost ~35 games in a row to once again, fall into silver 4-5 MMR. I just got out of my 10th loss in a row after once again entering my series for plat 4 and being demoted to gold 1.

I do not understand why I keep having the odds stacked against me like this. I do ok for most of my games, I don't ever reach 1v5 carry status, but I don't feed like crazy either. Then I hit my promo series and I'm matched with people in challenger or something. My KDA's show it, I get absolutely shit on out of nowhere. I'm not saying I don't get outplayed when I lose, but I don't get why I'm playing against people with similar MMR and then all of a sudden I'm playing against people with mechanical skill far beyond mine as soon as I hit as series and then even after I fail it.

I play ranked almost exclusively. I do it to avoid a lot of the negativity that comes with norms. With this most recent 10 game ass beating into plat->gold demotion, I genuinely feel like I'm being punished for playing ranked and honestly don't really feel like playing League anymore. It's either wacky antics in norms, or get poops made upon my chest in ranked, and I don't want to go through another 15-20 losses before I can try to climb my way back up to plat again to go through this a 4th time.

I won't lie that this is just a QQ thread, but ugh, I don't know where else to QQ about this system that hates my guts for being successful ;C