Thr is a mechant code need to be key in during registration
To avoid ppl stole the card from store/resell those sim card.
So i think u can only activate at the kk mart that u bought the sim.
Even other kk mart also cannot help u.

Hold your horses!

There are 2 steps before the card can be used:
1) Registration
2) Activation

Don't get the 2 confused or treat them as 1 combined step. (Having said that, I'm not surprised if some CSO don't even know the exact term to use.)

Dealer will register the SIM card for you, and most do the activation too. But I've come across some dealers like those in marts, rest stops, etc, who give customers the option to do the activation themselves. On the pack, you can see an expiry date - that's the date by when the card has to be activated.

ON the pack too, the instruction on how to activate the SIM card. You can either choose to follow that step printed there, or just make your first call from the card. I've just helped a friend activate his Digi card a couple of months back by making a first call, when I was too lazy to take out the pack (the cardboard holder where the SIM card is found) from my bag. I activated my own card using the step printed on the pack when I first bought it.

So the cashier didn't register your SIM card at all? 

Wait, weren't you puzzled when the cashier didn't ask for your IC?