Notwithstanding anything contained in any law for the time being in force, no proceedings for recovery of any amount under sub-section (7) of section 50 or under subsection (6) of section 51 shall be initiated after the expiry of seven years from the date the amount becomes due for payment :

Provided that when an appeal or revision has been filed, the period of limitation shall run from the date on which the amount due is finally determined.