Is paying the amount of debt owed on a credit card, which includes late fees imposed by the bank, after canceling the card, a sin?

Imposing a fine for delayed payment of a debt is precisely the forbidden usury (riba). It is impermissible to deal with such a card. What is obligatory is to repent to Allah Almighty for past dealings with it, to cancel the card, and to refrain from using it in the future.