GST Refund application rejected due to delay

Shrey Laddha (CA Practice)     10 February 2021

Issue: GST REFUND application on account of inverted duty structure has been filed by him for Dec 2018 to March 2019 in single application on 20 dec 2020.

In these months due date for Dec was on 19 dec 2020. And due dates for other months were not lapsed. 

But officer rejected entire application saying that application was not within time limit. 
Can anyone suggest any remedy or any case law?