Notice recovery amount payout - demanding a full recovery amount plus 18% interest for a year

I joined a big Indian company almost 1 year back. I received half a month's salary. Then after a few days, I resigned from that company as I was getting a great opportunity. After 10 days, got approval from the manager. Before I was considering it as early relief from the manager but at the time of submitting all the assets, I was told that notice pay recovery for 20 days will be there. I got a mail from the company for a recovery amount of around 30K (GST included) almost after 1 month. I didn't reply.

Then got a reminder on the same thread a couple of months afterward. But now after 1 year, I got a hard-letter from them, demanding a full recovery amount plus 18% interest for a year. Wanted to ask, is it legal to ask for recovery money if I just spend only 1 month in the company (including notice days)? If it's legal, do I need to pay the GST plus interest as well?

Pl check your offer of appointment as to the notice period during the period of probation. If you have accepted the offer or any other document (like service bond) containing such a term then you are legally bound to pay the salary for remaining notice period. As regards interest, payment of interest follows when there is delay in remitting the due amount.
But it is not likely that the company may pursue litigation against you to realise the amount as the cost of litigation would be more. You can offer them to pay the 20 days salary subject to closing the matter. It appears, you were relieved from service without any mention of dues towards payment of remaining notice period. So it will be a good point in your favour in case there is litigation any future

Dear friend,
Just give a try. Why don't you meet the concerned and try to reach a negotiated settlement? You may gain some advantage. There's no need to shy away in solving your issues.

Check your appointment order first. Check the Notice period conditions. As per CGST employment services are exempted from GST. However providing cafeteria, recreation, sports facilities to employees will attract GST.