Company not giving relieving letter and asking me to come back to work

I had worked for 4.6 years in an organization. And in this pandemic I was bit upset with my health conditions and had to leave the company after serving 23 days of notice period but soon I left the company the employer said that theyre considering my case as absconded. Now in this case I requested them for 3 weeks and then I sent my employer a legal notice demanding my relieving letter and my previously blocked salary and PF, But I left the company on a good note saying I’ll pay for the rest of the notice period also. Even though they refused and in return to my legal notice they replied with a legal notice asking to come back for work in 3 days for which if I fail then I had to pay Rs.5,50,000/- and also blacklisted along with proceedings. Please help me. I am not understanding what to do ? Whom to go for help, Whatever I do now will become a huge pay for my career. There were deductions in the salary from 6 months and also they company denied to give hike and kept my last months salary on hold.