FINAL FANTASY XV POCKET EDITION HD

I have played that area a dozen times to get this achievement watp killing more than 8 of them and the achievement refuses to pop up each time, idk whats up with it not giving me the Achievement that i should have earned by doing it multiple times by redoing the whole game a dozen times to try and get it. So if theres something that i am doing wrong or am not doing please lemme know so i can do it the right way and get the achievement finally.