GST return default notice

Dear experts,

I have received a notice in form GSTR-3A for not filing return under section 46.
The notice requests me to file return within 3 days.
The notice was received on 14 August, 11 am.

My chartered accountant is also not responding.

Is it some major issue?
If I file my return today will it be counted to be filed within 3 working days. ?
Does 3 days means 3 working days or not since 15 August was national holiday and 16 was Sunday?