I need help!

Is this broken or something but just now i played ranked using leblanc, and i was against a malzahar. I brought Cleanse instead of Ignite, cause i know that if malzahar ults me, then i will get surpressed and i won't be able to move. I spammed my F button for cleanse but nothing work. Is this like a Riot glitch or I cant cancel malzahar's ult using cleanse? Please help.