IS RIOT SERIOUS??

I started playing ranked flex and won 7/10 games got placed gold 1.Nothing bad about that (I finished plat 4) i thought to myself and rushed a few games and went promos for platinum in just 2days.Suddenly today i log in and it says you are required to play one more game in order to be placed again.I say why not thinking foolishy to myself that i will be placed minimum gold if i lose or straight to platinum if i win.Went into game carried hard and won game...and what happend you may ask?????? I GET PLACED IN SILVER 1...WTFFFFFFFFF??????????????????? HOW IS THIS LOGICAL?????NOW I HAVE to waste my time with silvers and golds to get back to platinum this is so wrongg ritooo plz!!!