Broken MMR system for Bronze

I've been promoted to bronze 2, 15 times. I've never been demoted to bronze 3. I know this means I should belong in this division, however after winning series, I will successfully get into 3 subsequent games where there is either a troll (read: "Ezreal support") or a smurf on the other team that goes 19/3/10. Or a smurf on my team throwing the game. (read: "try to get to nexus through mid lane as leblanc or singed, with mid Tier 1 tower still up")

I lost my series for the first time, and went all the way back to 60 LP. How does losing a series (with a free win) drop me 40 LP. when I can at max only win 18.

Please do something about the griefing smurfs, that will lose intentionally 3-4 games in a row just to make sure they drop a division. One guy I reported for intentaionlly feeding, then looked at his match history, and he won 15 in a row, and my game was his 3rd loss in a row.