Aside from a reading of your employment agreement, the company may also look into any communications that you may have had with them, to conclude whether they can recover any amount from you as compensation. If there is no such term in your employment agreement, then they may not have a strong case as they would not be able to file a suit for breach of contract.
The fact that you have not signed on stamp paper does not significantly increase your chance of success since the same may be rectified by the Company upon payment of a certain penalty along with the stamp duty so you should not rely on that fact.
You may contact me over LinkedIn in case you would like to discuss this issue forward.
Please see your appointment letter for details.