Please suggest.

[ For short, read last portion. ] I worked for this marketing agency, D. M. , for over 7 months and I haven't received my FNF and other documents like experience letter and relieving letter or even appointment letter. I gave my resignation after being continuously pressurised to resign or overwork for around 3 months March/April-May and being denied my promised salary upgrade to my previous salary prior joining this agency.. on 4May. Before joining, I was asked to work for 20,000/- instead of my previous salary 24,000/- for 3 months, saying that I would be working for 24k after 3 months. I said I wanted it in written and the founder Mrs. C said that they will mention it in appointment letter but they never gave me my appointment letter. I talked to them everyday and asked about it in the starting 2 months then she said she will hire an HR to do all document work but never did. Then after 3 months I asked about the 24k or 25k salary everyday. The only answer I got for the next 3 months was that they are very busy and unable to discuss the matter internally. Whenever I asked about it, I was mentally harassed on the following days by rubbish words like my work is not good or that I don't deliver on time when actually I always worked from 10am to atleast 8pm almost everyday since day 1 of my joining. This was not happening just with me but all the other employees and everyone eventually left the company anyhow they could. I wanted to be a decent employee so that I can receive my experience letter and relieving letter when the time comes and so I resigned on 4May and was supposed to leave on 4/5june but they requested me a lot to stay. I told them that I had to absolutely leave due to some health condition and wanted some time off for myself. But they convinced me to stay for few more days and I agreed for 10 days. My last working day : 14 June 2021 and joining date: 21November 2020. I haven't received my FNF ( June salary) which according to their policies was supposed to be given after 45 days but now it's been 3 months and I still haven't received my 14 day salary or any kind of documents. The remaining salary amounts to somewhat 9,334/-. Please tell me what I should do.