Customs duty recovery rules: notice periods, voluntary payment, and fraud-based extended limitation govern short-levy and refund errors. Recovery of customs duties and interest that have not been levied, not paid, short-levied, short-paid, or erroneously refunded is governed by a notice-and-determination mechanism. In non-fraud cases, the proper officer must serve notice within two years from the relevant date after pre-notice consultation, while fraud, wilful mis-statement, collusion, or suppression of facts extends the period to five years. The person chargeable may make payment before notice on self-ascertainment or departmental ascertainment, and timely full payment after notice may conclude proceedings and avoid penalty in specified cases.