Full n Final settlement - instead of giving me my one-month pay, they have asked me to pay 41k

I joined HCl on 16th august and left on 7th June. served complete 3 Months Notice period. After 1 month of relieving, when I inquired about fnf as my 1 Month salary was pending with HCl to Pay. Instead of giving me my one-month pay, they have asked me to pay 41k in return of my offer letter. When I consult the same with fnf team, they said that I left the origination prior to one year and have to pay this amount to get an experience letter .
My concern is that this information is not mentioned in my offer letter that I have to pay this much amount if I will not complete 1 yr with HCl, neither same has been conveyed to me. On what ground they have asked me to pay 41k and deducted my one month salary

Dear Noopur,
Did the management impart you any exclusive training with salary soon after your appointment? Even then they can not ask you to pay the sum for issuing experience certificate when the condition was not put in the offer letter or conveyed to you when you submitted your resignation or while serving the notice period of 3 months. They raise such a demand only when you ask for the unpaid salary. Therefore, It is an act of illegality as well as unethical. Send a legal notice to the management to disburse the unpaid salary along with experience certificate.

Hello, My previous employer HCL Technologies has unlawfully deduced in my Full and Final settlement. I have served the required 90 days notice period. There is no mention of such policy in the offer letter or joining dock agreement. I would like to explore the legal scope as I am sure I won't get the solution from the HCL team. There are multiple people having the same issue.