Any unused credits can be refunded within 14 days of purchase. Open Settings → Billing → Purchases, click the receipt you want to refund, then Request refund. The refund returns to your original payment method within 5–10 business days.
Used credits aren't refundable, but if a tool failed (say, OCR returned garbage on a clean scan) you can flag the run from Settings → Billing → Usage and we will credit them back manually within one business day.
Subscriptions can be cancelled any time from Settings → Billing. See the 'How do I cancel my subscription' article below for the step-by-step.