Training cost recovery - AI asked us to sign a bond (which was never mentioned before or even in advertisement)

I am working for Air India. I joined AI in 2010. Before joining I have to go through a selection process where they mentioned that pilot training cost to be borne by candidates and we spent our money for Commercial Pilot License after which we were given joining in 2010 . Just before joining AI they have asked us to sign a bond (which was never mentioned before or even in advertisement) for further training. With loans running we have to sign it in 2010 as loan amount was swelling up.

Now after 13 years I am leaving Air India and they want to recover that money or they will not give me relieving letter. Please help!
In between the company unilaterally changed our salary structure in 2014
In between during COVID company has unilaterally deducted salary as economy measures.
In between they took 4 years from 2010 to 2014 to keep me as trainee pilot for their own mismanagement.
In between AI was privatized in Jan 2022 which is now under Tata

Hi

What was the terms and conditions of the bond you had signed?

For Commercial Pilot license you spent from your pocket and what is the necessity of recovery of training cost after 13 years of service?. Not ethical. You can defend this legally.

Well after Commercial pilot licence there is type rating training which was done by AIR INDIA. I was asked to sign this bond of 7 years and the type rating cost in 84 equal installments which they didn't deduct as we challanged in court that it wasn't there in our hiring advertisement. Unfortunately court dissolved that case and asked to refile with new owner.
Now they are arm twisting to retain people by asking to pay that typerating training cost