Diamond V Smurfing

How are you a smurf with around 1000 normal games, over 200 ranked games and not only stuck in silver, but dropping steadily, only winning 3 of your last 10?

Exposed

I've seen him posting about how he is a diamond smurf for a few weeks now but he can't get out of sliver so i doubt he is on a friend's account. He used to post looking for other smurfs to dynamic with, I played with him once on my smurf and he played like a typical silver.