Stuck in a Bad Spot

So I recently started playing League seriously this past August. I had played the game before but I found myself doing terrible in even bot games but then I found champs like Annie and Morgana who I could play really well. Unfortunately I began to stick with a few champs early on and that meant that I didn't play that many different champs overall and therefore don't really know the skills of all the champs and their utility in battle.

Things were going really well and I would win pretty much majority of my matches with champs like Annie, Malphite etc but recently I hit level 30 and all of a sudden I am getting matched with golds and silvers who I don't think I am as skilled as. I decided to try Ranked as soon as I hit 30 and I went 5-5 in my placements so I was actually hopeful I was going to be put in bronze where I think I belong but somehow I got placed in freaking Silver II. Every game I end up having people rage quit or flame at my team including myself for being terrible and essentially I can't try out any new champs now because I'll get flamed in ranked or normal. I want to get better but I don't think I'm learning anything from having teammates who just flame and quit on me when I'm trying to learn rather than helping me. I recently tried out Twitch and I didn't do so well and my support randomly just starts roaming and taking jungle while flaming at jg too for not ganking enough. How is that helpful at all??? At least in bronze I can actually test out new champs and learn their mechanics while knowing that I can play with decent proficiency and not feed and then when I'm ready I can begin to climb rank. Bot games (intermediate) is still too easy and not representative of my normals or ranked matches.

Please Riot, add a mode that helps for practice with new champs because I don't think I am where I belong and my rank definitely doesn't reflect my skill. Maybe smarter AI bots (even better than Intermediate?). ARAM is nice but the champion is random so it's not exactly efficient if I'm trying to learn one specific champ's mechanics. My friend who first taught me how to play Annie this past August is Silver IV and I doubt I'm better than him.