Why my portable charger was confiscated from my checked-in luggage?

When I arrived to the counter to check in my luggage, she gave me a paper that says to put portable charger to my checked in luggage as it is not allowed in my carry-on luggage. I did it according to their advise. However, when I arrived to Singapore I found a paper in my luggage informing me that they had to confiscate my charger. Did I miss something in the regulations? Why they did not inform me properly during the check in that something could go wrong? Thank you