Harassment and legal threat by Client to freelance graphic designer

I'm a freelance Graphic designer from Kolkata. I had taken up a design project in 2017 (for 8 package designs for Rs. 35,000) with 3-4 rounds of changes and to be completed within a period of 8 weeks. There was no signed contract. In 2019, I tried to persuade her to sign an agreement. She kept refusing to the terms. Instead, she sent a lengthy contract drafted by her lawyer — the terms of which, I did not agree with. Eventually, nothing was signed. The work kept going on. The project got over last months — with the client forcing me to work on 28 packaging designs, with 9-10 rounds of changes. I sent her the invoice (Rs.80,000). She refused to pay and insisted I give her all files at the original cost of 35K. She has now involved her powerful lawyer and he has emailed me a 'pre-initiation notice' threatening initiate civil and criminal proceedings against me for extortion and damages, if I don't send the files within 72 hours. Please help.