Not getting experience letter even after serving 1.5 years of notice period

I have worked in company for 3 years and after 1.5 years I have told my boss that I don't want to continue. He insisted that he can't do anything right now please give me time of 3-4 months. So I have waited and then again went to him and told that I want my final release date and again he said I can do anything right now as of financial months. I waited again and then during covid I sent resignation email after that I have server 3 months of notice period as well. After notice period - He said I can't let you go know you have to server 1 month more or get take this package. As it was covid period so I thought of going with package. He said that you have to work until this month that's final. So I agreed and when final month came I told him I want to go now. He said I can't you have to transfer knowledge and you have to stay for 5-6 months. I don't want to work their anymore. So I stopped going to office. He has not given me 20 days salary and my 3 years of experience letter is also. He just keep on threatening me that I'll do this or I'll do that. I will backlist you so don't get any job. I have all the proofs since when I have talked to him about resignation and I don't want to continue anymore.