Validation of levy and collection of duty

and collection of such duty had been included in, and this section had been in force when such duty was levied or collected and all things done or taken by any person in connection with the same shall, for all purposes, be deemed to be, and to have always been, done or taken in accordance with law; (b) no suit or other proceeding shall be maintained or continued in any court for the refund of any duty so paid; (c) no court shall enforce any decree or order directing the refund of any duty so paid; and (d) any duty which becomes due to be recovered in the manner provided in the said Act and the rules made thereunder: Provided that it is hereby declared that nothing in this Act shall be construed as preventing any person from claiming refund of any duty paid by him in excess of the amount due from him under the said Act.