Hey @Hansuhyun,
Welcome to the Community!
I'm sad to see you left us. You would usually receive a final invoice on the billing cycle after the cancellation.
This final invoice will have any billed usage, prorated adjustments and of course if you have any balance left owing on your device; it will also be on this final invoice.
Did you get a chance to check out your most recent invoice to view the details of the charges? You can see more about this here. 
