Resignation

Good Afternoon Sir, I was working with an event Management company for the last 7.5 years , post the pandemic the company reduced our salary to 50 percent . I Resigned on the 29th of November 2021 and asked the company to relieve me in 2 days because we had no work for the last 10 months and there was nothing serious in terms of handover , in my resignation email i asked mentioned that the cut in salaries has been serious stress and its taking a toll on my health , I was detected with Covid and was admitted in the hospital for 14 days ( there was infection in my lungs). Post my resignation email I got a reply from the CFO ( Consultant) I was neither reporting to him ,nor there was any communication in the company that the CFO is handling HR related matters .The CFO accepted my Notice period and asked me to serve a notice period of 45 days. My question: 1. Is the CFO Authorized to send me a reply on my resignation email. ( I had not marked my resignation email to the CFO) 2. While going through the employee handbook the clause says ( The resignation clause says your supervisor or HR should acknowledge your resignation email) 3.Is the company correct to ask me a notice period when they are paying me 50 percent of my salary . 4. when I followed up with the company for my F & F , I received and email from the director on the 7th of February 2022 (ie :40 days after my resignation) asking me to compensate for my notice period . 5. Can I ask for Gratuity. 6. Can I sue the company.