Employer relieved me early and did not let me serve my full notice period

I am a market research employee with 6 years of experience. I was recently put under PIP(performance improvement program) by my employer although my performance from the last 6 years has been great. I was promoted twice during my tenure at the company. Post receiving PIP notice I felt humiliated and questioned my employer for the notice to which his response was that I am not putting enough efforts to generate revenue. I felt disgusted by the response as I have been a hard working employee and served the company for the last 6 years with utmost dedication(I even received an award for my commitment towards service in 2019) I felt my self respect was being questioned due to the PIP notice following which I voluntarily resigned as I did not wish to continue with my employer after knowing his thoughts and what he thinks of me and my service. My notice period was 90 days but my employer within 45 days sent me an email of my relieving for which I was surprised at first but I understood his intent and accepted the terms as I did not wish to continue with people who think low of me even after all these years of service. I would also like to highlight that my appraisal was due a month before I received the PIP notice and since appraisals in the organisation are never on time I did not get into a discussion with the employer as to why my appraisal is not being done. I accepted the early reliving as I could not stand the negative work environment which was created by the employer and I understood his intent that he was pushing me to resign so that he does not have to lay off. Also during the PIP period I was being given an unachievable target which was impossible for me and my whole team and the condition under that PIP email was that I need to achieve this impossible Target or else the employer would take action against me which could also lead to termination. Since I resigned willingly keeping my dignity intact I did not ask for any compensation from the employer for reliving me early as I felt it would seem like begging for money although I understand that there is a provision for severance package in case your employer terminates or relieves you worngfully. I would like to ask for professional guidance on this matter seeking help if I should send a civil/legal notice to the employer seeking compensation for early reliving or not. Thank you for all your help in advance. I thank you for taking the time to read this query.