How much to pay for Unserved notice period - is that a Government rule?

I was working in an IT private company in Bangalore. The official notice period was 2months but I served only one month. Now in the Final settlement the company is telling me to pay for that one month unserved notice but the main issue is, HR is asking for that one month Gross salary. And on top of that they add 18% GST on Gross salary. So I just want to know is that the Government rules because when I asked the HR , she told it is. So what should I do now. Please suggest . And if anyone have the right info about please provide.

How has salary been defined in your appointment order?
How many days notice is the company expected to give you in case company wants to terminate employment?

Hi, Company has not terminated me. I only resigned.
And salary has defined from Gross after some deduction (PF, tax) monthly net I was getting. Are these related to the question I have asked!? Because I want to know is that legal that they can ask me Full Gross salary 30 days n including 18%Gst on that??

Hi
Regarding the gross or basic salary to be calculated for notice period depends on your employment letter, there is no GST applicable for salaries to employees. Ask them to show the rule under which they are to be paid. [GST]. If they give it in writing let them deduct and lodge a complaint with the GST authorities. Though employee is said to be giving 'services' to the employer it is not the same as under Goods & Services Tax rules of services. Only consultants like CAs, CS, Tax Practitioners are levied GST for their professional services.
Thanks and Regards

Dear,
First of all there is no question of GST. because, on salary, GST is not applicable.
please go through, you appointment letter carefully, normally, notice period for one month or two months is given, after confirmation letter, have you received the confirmation letter or you were on the probation period. because, during probation period, notice period is very less, either, 15 days or 30 days.
Thanks

Hi all, Thanks for the replies. About GST applicable proof they have sent me a mail saying that their auditor had told to calculate. And I am not in provision period. So Notice period is 2months only. But about unserved notice period payable no where it has mentioned. I have requested to Head HR also but he had also saying the same.
So about unserved notice period payable where they should mentioned because I didn't get any information on my employment offer letter!

Dear Freind,
The unserved periond is nothing but shortfall in notice period, which needs to be waived by your Employer or equivalent salary has to be paid by you please.