yasuo can't ult ?

I just came from a game(normals). I was playing yasuo and at lvl 6 when i knocked my enemy up i couldn't ult.first i tought maybe it wasn't in range or so or maybe i didn't pay attention if my enemy (garen) silinced me. But the second third and fourth time it was pretty obvious that my ult wasn't working. bcus i wasn't silnced and i was in the range of my ult. Is there something going on riot?? , fix this please.