rank system

I am a plat 4 player but i dont know why in solo q i met gold 5 or silver player. during my plat 4 promotion, i met silver and gold teammate and therefore i fail my promotion. 2 days later, same situation happens to me and makes me drop to plat 5 almost back to gold by the way. l was 20 wins> loss, so i dont know what they mean by low mmr. Futhermore, if u say i lost a lot recently then ill take it if i matchup with gold player, ill be fine but silver is way too far especially trolling me. I dont get what does this system works, and recently i got 8 wins in plat 4 and i just matchup with gold 5 teammate with 12 death took my victory away. I mean if you say that gold 5 player wins a lot recently therefore can matchup with plat player, then y i got 8 wins recently cannot matchup with some daimond 5 player. Put in this way, if im plat 1 player with great mmr(win 8-10 recently), so i could matchup with master player who also has bad time in their rank lately? or daimond 5 player matchup with challenger player? Riot please take this issue seriously and stop using double-stander with high elo players and low elo players.