Won my series but didn't advance. @riot

So I lost my first series from silver 3 to silver 2 due to intent trolls, which was unfortunate. But I got back into series easily and was granted a free win.

I then played 2 games, lost the first one and won the second one. However I didn't advance to silver 2.

With the free win, my last game should have promoted me to silver 2.

I'm failing to understand why the game still registers me as silver 3 100lp, this shouldn't be the case.

I won my series fair and square, and now I feel like if I play another and lose I'll be cheated out of my promotion. This really isn't cool.

Can anyone explain?