Matchmaking

So recently, I've been trying to get back into ranked League of Legends because I like the competitiveness of it despite my lack of playing it over the years. Any-who, I will get straight to the point recently, (a Kayle and just now, a Cho'gath) have been placed in my high gold ranked games, while they are silver 1 with REALLY low win rates (ex. Cho'gaths was 14% and he wasn't duo with anyone) How does this happen? How do they get into my games? Its throwing my LP away for free and frankly really frustrating to deal with and I think this needs to be looked into.