You need to remove your credit card information from your Heroku account.
For a personal account, you may remove your credit card from your account via the Heroku Dashboard billing page. You can find more information about the Remove Credit Card feature here. You may need to downgrade apps to Free Dynos and delete add-ons before you can successfully remove the card.
Note that you will not be able to add a new credit card for up to 30 days after you remove the current card. If you will need to change the card on file sooner than that, use the Update Credit Card option instead of Remove Credit Card.
Heroku Teams cannot remove their credit card. Workarounds include turning off paid services to stop billing, or deleting the team account to remove personal information from Heroku.