Legal notice for Abscondment

We are a CA firm based in Delhi. Our Senior Executive - Finance & Accounts absconded on the morning of Sep 9 after leaving his laptop with a peer before official start time. Neither did he inform his Manager nor did he inform HR of his intent to resign. Further, he decided to abscond only after processing payroll & ensuring that he received his salary. On being handed over the laptop by the peer, the HR Executive at the firm, tried reaching him several times on the same day & the next but there was no answer. Moreover, after several calls from HR, he decided to switch off his phone. I had joined as HR head on the day he absconded & since he was unaware of this, he answered my call on the evening of Sep 10. When I told him who I was, he hung up. Consequently, I tried reaching him multiple times but he kept cutting my calls. Post the call, I sent him an official warning mail. It was only then that he reverted to us on Sep 11, saying that he absconded because of the rising cases of Covid in his area & that he was willing to serve notice working from home. Since, his area was not designated Containment Zone & he was dealing with confidential financial & accounting data, we were not comfortable with him working from home. So, we asked him to come back to work at office and serve his notice period as per his employment agreement. We also gave him an option to buy out his notice period. We further added that in both cases, he would need to do a complete handover of his duties. We told him that he should revert to us within 2 working days. But there was no further communication from his end. So, I called him again on September 15, 2020 to discuss the further course of action. In the midst of our call, he handed over the call to his mother. The mother was politely to told to hand over the phone back to her son as she was not employed at the firm. She refused to do so and was very aggressive and confrontational and accused us of harassing her son and the family. I'm very confident that she was not aware of the facts of the case. So, once again I wrote a mail to him to attend office and complete the handover and his notice period. I reiterated that he is free to buy out his notice period, if he so desires. There has been no communication from him since then. We would like to serve him a legal notice.