Employer Sent legal Notice

Dear Sir / Mam , I was worked in One startup company from Aug 9th 2021 to Sep 3rd 2021 -1 month only( Named as 'A ' - Don't want to reveal the name ) .I worked as an HR position but they gave me irrelevant works other than HR role and put pressure on work areas and extending our work time. After few days ,I got to know the company has not good background and almost no past employees were there .All previous employees were left in a month itself .CEO daily force me and threaten me that company doesn't received any projects and. U were not performed well to get clients. He changed my actual role and revised my salary from 20,000 to 10,000 telling as low performance. .So I quit my job there. Even though I left by sending proper relieving mail ,he threatens me through call asking bla blas about other employees exit. Actually he put pressure on all employees and salary was also not given for us so we left. But he threaten me that I am spreading rumors and I am responsible for employee loss and I am not supposed to join any other competitor company for one year. He send me legal notice too for the employee loss but it truly depends on his own pressure given to all employees. Please help me how to solve this legal notice.