Send a change request (/help/change-request) with your receipt number. Our records are checked the moment you send it: a duplicate charge, a charge after you cancelled, and Priority Review that never turned on are refunded automatically. A person answers anything else — a different amount, a charge you don't recognise — within two business days.
You never have to ask us first: you can dispute a charge with your bank or card company at any time, and doing so doesn't affect your account. But while a dispute is open, the bank's process decides it — we answer the bank with our records and can't also refund the same charge. A change request is usually faster.
Send a change request: billing mistakes our records prove are refunded automatically, and a person answers the rest within two business days.