Notice period clause in my offer letter: “You will be considered

Notice period clause in my offer letter: “You will be considered as confirmed in service only when you are intimated to that effect in writing. On confirmation, the notice period for separation on either side will be three months. You will be required to attend office throughout the notice period. In the event of operating the provision of payment in lieu of notice, the notice pay shall mean the full monthly salary, including any other allowance payable. The option of offsetting the notice pay, partly or fully, by way of payment in lieu of notice period or by adjusting the privilege leave at your credit is at the sole discretion of the company keeping in mind business continuity.” I had served 22 days on notice period and get relieved from my job after handing over all the assets and task to immediate superior. My previous company had adjusted my salary for 21 days, my bonus benefits lying with them and adjusted EL and now asking for a recovery amount of Rs. 42,000/- and threatening to go in legal if I don't pay them. They had issued a demand letter with time limit of 1 week. I resigned from the company because they had issued a warning letter and raised eye for not being ethical. Since I don't wanted to work with such company, i decided to resign. Also requested one of my previous employer to join them, they had accepted the request and now i am working with them since 3 months. I had discussed with them over phone, but they are not ready to accept and again threatened to wait for legal consequences. I am seeking advice on the action, which I can take on this issue. please guide. Thanks in advance.