Company sent me a mail to pay lieu money - What if I don't pay any money?

Hi , I left my company without any notice period because I was depressed as they were forcing me to achieve the sales target , now after 45-50 days they sent me a mail to pay lieu money... and not doing so will invoke legal proceeding. What if I don't pay any money?

Dear Sir, Kindly refer your appointment order employment terms and condition. if there is any clause for notice period base on you make your judgement.

If you had to leave due to depression, and if you had met a medical practitioner for diagnosis or treatment of the depressive condition, you could check on whether the doctor had considered you unfit for work then. If a medical certificate confirming that post examination the employee was found unfit for work, could be submitted then this could create medical grounds for a notice period waive off. But please do be careful not to submit any fake certificates.
With regard to the mail for you to pay them money, the company has to follow a number of procedures for this first. They have to first send you letters of concern in hard copy to your residential address stating that you have not reported for duty to serve your notice period. This has to be done at least within 14 days from the day you last attended work. If they do not receive response to the letters that they have sent, then they can conduct an inquiry in your absence and ex-parte issue a dismissal letter to your address. It is only after all this that any correspondence for retrieving damage can be initiated.
If you are not working anywhere else now, you can also offer to serve the notice period now in lieu of the amount to be paid by appealing against the dismissal.

Dear friend,
Rules are there in the realm of employment only to be followed and not to be flouted. If you did not like the job for whatever reasons, you are at liberty to put down the papers subject to the unilateral exit conditions of your contract of employment. What prevented you from tendering your resignation with sufficient notice or in case of any personal inconvenience like the one narrated in your post from buy-out of the notice period?
Of course as the other learned friend has suggested, the management can treat you as an absconder and terminate you after following a due process of disciplinary action in case of your failure to comply with the latest notice. Certainly it would adversely affect your future employment elsewhere.
Therefore, it is better to resign formally now by paying the notice period amount and make your exit peaceful.