You can send a communication mentioning your previous mail stating that you have already tendered your resignation which unfortunately could not get a proper response from the company. 

You can also state that since you are in the circumstances of joining a new company,  your last working day would be.....

You can stop attending office after that. 

In the same communication which can either be sent by registered post or handed over in person,  you may demand settlement of F and F as well as the experience and relieving letters. 

1. Since you have already created enough evidence for the management to reply to your queries, you can drop an email saying that no liability against you can be made out concerning dual employment and with the induction in new company on 14th March.

2.  It will be considered by the court of law as the genuine trial by you and will not be considered as an act of intimidation by you.

Resignation submitted in Jan 22, notice period served, subsequently some complication arose and resolved. On your side you have, for all practical and legal purposes terminated employee-employer relations. Now employer is not intimating  full and final settlement. You can put in a email declaring your final cessation of employment. There is nothing rude about it, keep your email polite. This will save you any future legal trouble.

Inform the company that you have completed notice period and you would not be coming to office from 13 th March 2022 and to give you experience and reliving letter 

you are at liberty to join new organisation

You can drop such email but it will be considered in merits only

You have completed the 2 months notice period 

you are at liberty to join another organisation on 14 th 

Even if you don't receive the confirmation from your present employer, since you have created sufficient ground to defend your stand, you will have the legal backing to join the new company on 14th.

Yes

If you have decided that 11th March will be your last working date, you may do not have to go back to work even if you don't get relieving orders by then.

You may leave a communication to the employer stating that you have stopped working for them from 12th onward and that they should settle  the F&F and other dues including furnishing the relieving letter and experience letter if any.

This communication would confirm that you are no more employed with effect from 12th March and that joining the new company on 14th March would not be in any manner considered as dual employment.

Dear Client,

                  Kindly try following up through mails and other possible means of contact the company and HR. Try to remain as much informed as possible about the situation and receive confirmation

Thanks & Regards