Employer not paying fnf what can be done

I had a very abusive ceo and she has abused almost everyone. The salary was delayed every minth 30 to 40 days delay. I finally quit the job due to her abusive behaviour and I was given fnf letter. When i asked for my fnf she said it will take 45 days. After 45 days when I asked her, she said will take time. She somehow read a chat between me and a colleague where i have used some slangs and abused me on phone again and not willing to clear my fnf. She is also telling that she will file a police complaint against me. I have proof that she keeps abusng everyone on face . Please let me know what can be done in this case.