Sometimes payment transactions cannot be processed at the time of invoice creation. This might be due to insufficient funds on the card, a declined card, or some other reason. In that case, we will re-try to process the transaction up to 10 times over the course of the next months.
If you canceled your subscription, but there was still an outstanding unpaid invoice, this might lead to a payment being processed even after your subscription has been canceled. You can see all invoices tied to your subscription on your payment settings page.