I lost 1 game at 0 LP and got demoted

How is this a thing? I played great to get to silver 4 and then I play a few and then 1 game at 0 LP demotes me? That has to be some sort of messed up glitch.

My second question is I won like quite a few games in a row and received a promotion. then suddenly something shifted and I had a ton more feeders in my games and ALOT more griefers. Such a considerable change in the game that I honestly don't want to play anymore. I've put alot of time and money into this game because I enjoy the challenge. When I die twice and someone starts dogging on my play style, or I try to jungle and someone has fed the enemy team 4 kills in less then 3 minutes and the entire team starts to blame me. I just want to know whats changed! Did someone report me and league decided to stick me in the que with trolls and feeders? or am I just honestly getting unlucky 6 or 7 games in a row.