Gone through your post. You have written, "Now the HR is after the pending advance salary and making a nuisance out of it by giving threats on and off."
The clarification is needed here. To recover the salary advance from the employee, it is HR's duty to follow up. The HR was doing their duty. If you wish to consider it a nuisance be as it may.
Why did your friend not serve a notice period? What are the terms of separation? What is the length of the notice period he was required to serve? What about the payment to the company in lieu of the notice period?
Did your friend raise grievance for his perceived injustice to him? If yes, then how did he do it and what was the reply from the administration of the company?
Now your friend may write a letter to the company explaining to them what dues he owes to the company and what company owes to him. He can work out the details on his own. Has he done that and if not, then why has he not done that?
Please clarify the above points.
From India, Bangalore