Repayment of erroneous drawback: claimant must refund on demand and unpaid sums are subject to statutory recovery. Repayment obligations arise where drawback and any interest have been paid erroneously or in excess; the claimant must repay the overpaid amount upon demand by an officer of customs, and failure to do so permits recovery under the procedure in sub section (1) of section 142 of the Customs Act, 1962.