Rammus taunt not working properly

I just played a game where my taunt as rammus didn't effect Katarina and only Katarina half the time, she would stop, hit me once, then continue on her merry way no matter what level my taunt was, even with the effect still playing over her head.

Also it didn't cancel her ultimate at one point during the game even though it forces champions to stop what they're doing and auto attack you.

I didn't know where else to report it.