They just swapped my phone housing with a brand new one.
They just blamed the cracks formed because of the casing that I'm using.
First time it happened, I was using a Rock brand hard plastic casing (frankly it was pretty hard and solid so I believed them)
Second time it happened, I switched to Rock QuickSand casing (I figured it would be better since it was made of much softer soft-touch material. This time I was starting to doubt it's the casing fault)
Third time it happened, I was using a generic no brand thin flimsy plastic casing (which is as flimsy and soft as paper)
This time, I purposely used my phone naked to eliminate all possible casing related causes. Yet it has happened again, for the fourth time even though my phone has been NAKED since the last warranty claim

-------------------------------------------------
I only dropped my phone twice before (both times when my phone was within 2 months old). But neither of those drops caused any cracking. Since then I have been very careful not to drop my phone or cause any impact to the phone (so far haven't drop it anymore since then

)
The first crack only appeared when my phone was approximately 5 months old.
Feel like sending an official complaint, but I doubt they will do anything since it's not covered under warranty as it is an exterior damage. The 3 times that I managed to claim warranty was because the people at the service centre were helpful and kind. They helped me claim under warranty even though the T&C said otherwise.
In that respect, kudos to Samsung service centre for having excellent customer service
I don't blame Samsung as I seem to be one of the only people who constantly face this problem over and over again.
Just bad luck I guess

Just wan to know .. usually how you carry your phone..... such as put phone in front pocket or back pocket (jeans) or shirts or handcarry ?