My ex employer falsely accused me and sent me a legal notice.

I worked as an intern at a company for 3 months and got promoted as a full time employee after that. After working for one more month, I had to resign from the company due to certain reasons and asked for an early release. On this, the HR sent me an email accepting my resignation and mentioned that they are releasing me the same day. They also mentioned that the FnF and relieving letter will be sent after 90 days. After 90 days, I didn't get any response from them, so I sent an email regarding that to which they replied that I didn't serve a notice period and didn't do the handover for which they will take legal actions against me. (To mention, the handover was done completely and notice period was waived off by them.) After one month of this, they sent me a legal notice claiming - I didn't serve the notice period, so I've been asked to give a compensation of 30 thousand to the employer. - I worked in the business development department and i was in discussion with a brand. After I resigned, my colleague took over the conversation but now the company is saying that there was a misconduct from my side due to which that brand suffered a loss of about 1.56 lakhs bh the month of November and I am supposed to pay the amount. (To mention, this is all false accusation.) - Moreover they are accusing me for sharing confidential information of the company after my resignation which is again baseless, false and without any proof. I don't have a legal background and I don't know how to proceed in this situation and also, what steps am I supposed to take. Please guide me on this.