If you need to cancel, you can do so before the expiration date. You can log into your Piktochart Account. Please click the profile icon at the top right of the page. Then go to Account Settings on magic.piktochart and click on Cancel Recurring Plan next to your Account Status. You will see this option on the Plans & Billings tab (to the right of Settings).
You will not be billed any further but will still be able to enjoy all PRO benefits until the expiration date of your last payment.