Trivectra

Well I guess my time has come. After 10 more Mankey's I got it.

With the quest Ash's Hat you're supposed to get the hat from a Mankey that's nearby. I've killed like 70 Mankey's by now and still don't have the hat. I talked to people who got it in like 2 tries. What am I doing wrong? I'm using a Mankey with Covet. (My starter is Pikachu)