I was in same boat as you are in. In November 2014 I got 30 in ISCA despite studying from study material.I can very well understand your pain as on date.
Then again, I started with ISCA.I gave it 6 full time readings. My advice would be, start with first reading a fresh mind. Give it 3-4 hours daily, for 15 days.After that second reading, try to remember the points of the topic. Give second reading 12-13 days. And henceforth subsequent readings according to your own satisfaction. Cram points, also have idea what is to be answered in explaining those points. Lay very special emphasis on topic of practice manual.
Doing this I was able to clear this time, scored 49 marks in ISCA. God's grace got out of this subject this time.