Section 20. Suits for cancellation or modifications of certificates

(1) A defaulter may bring a suit to have a certificate canceled or modified and for any further consequential relief to which he may be entitled. (2) Such a suit may be brought at any time within 6 months- (a) from the service upon the defaulter of the notice required by section 6 or (b) from the date of the determination of a petition denying liability under section 8 [x x x], or (c) from the date of the protest lodged by him under section 15, [or] [(d) from the date of the decision of an appeal filed by him under section 23-A]: [x x x] Provided [x x x] that notwithstanding anything contained in this Act and in any other law for the time being in force, the defaulter may in a suit instituted under this section, prove that nothing was due from him on account of the public demand or that the amount due was less than the amount stated in the certificate.