Last date of filing of Return SUNDAY

mantrana tsg (9 Points)

17 May 2022  
During COVID CBDT extended due date for filing ITR of individuals upto 10thJanuary, 2021,which happened to be a Sunday. CA office was closed. ITR was filed on 11thJanuary, 2021.
Income Tax department treated it as a belated return and imposed penalty of Rs. 10000/-
My query is that since Last date was Sunday añd ITR was immediately filed on next date 11th January, 21 same should treated as having being filed on due date.
Please give your comments along with any available case law.
Thanks🙏🙏🙏