Only an account admin will be able to cancel a card.
As an admin, you can cancel the card via the Business Dashboard.
Steps as below:
1. Log in to your business dashboard
2. Go to "Cards"
3. Choose the card you would like to cancel
4. Click "Cancel Card"
Please note the card will be cancelled at the end of the month and any money left on the card will be returned to the account within 7 business days from the date of the card cancellation.