Hi there HoangPhu,
Are you seeing that a payment was sent for your order? If so and the order has been cancelled then you should check to see if your payment is showing as refunded. If they were using the order and authorisation option then you should be seeing the authorisation and order showing as cancelled. If the payment is showing correctly then I would recommend checking with your bank to see if they can locate your refund for you. I would also recommend checking how you funded the payment as if you funded it with your PayPal balance then your refund will be added back to your PayPal balance.
I hope this helps,
Paula
