Legal notice received for retrieval of notice period amount

I joined a company on 18/12/2019 and on 22/01/2020 I sent formal mail of resignation and handover all company properties. I didn't show up in the company afterwards. Now after 2 years on 12/04/22 I received 2 letters from the company for the recovery of the notice period amount and very next day received legal notice from a lawyer to pay the amount within 15 days by a demand draft. Failing in doing so they will charge me 24% from the last day in their records and will file a case against me in court of law. Also in the offer letter it is mentioned that ""Your employment with the Company can also be terminated either by the Company or by you by giving the other party three months advance notice. If the Company terminates the employment and decides to relieve you before the completion of the notice period, the “Basic” component of the salary for the balance notice period would be paid to you. If at your request, the Company agrees to relieve you before serving the full notice period, you will be liable to pay the Company the “Basic” component of the salary for the balance notice period."" Can someone guide me the next steps.