Manager in one of previous companies, India, refuse to give experience verification letter for my PERM application.

What could I possibly do by asking the HR of India office so that I can get the experience (skill & technology) verification letter, it involves past managers approval, and I am stuck at it? **Background** I have been in software development role all my career. I worked for this company in India for 4 years. My mgr was also Indian. When I told him I want to go for higher studies in the US and I need his recommendation letter, his behavior started to change and a month later he put me in PIP. I still managed other 3 recommendation letters and finally did my CS MS in the past. Also, at that time in India, I somehow managed to survive the two months of PIP without getting terminated. It was the most stressful time when I had to beg him for time and I will do anything he want. I worked 12 hours in office. Also, in those two months, I completed my university applications, and at the same time had to study for tech interviews. Within those two months, I managed to get 3 low TC jobs and 1 higher TC job in India. I resigned on my own but after that, the same day, he showed me that he is marking me URA (I can never work at this company, it is in top 10 US companies, anywhere in the world again now.) I swallowed it! I worked at some other company for 6 months until my F1 visa approves. After so many years now, when I needed to submit PERM application letters. I reached out to him on LinkedIn, office email, personal email, and via company hr, all the time he refused to reply to me, and he would visit my profile on Linkedin and pass. HR stopped responding to any of my emails which involves my past mgr. I worked there for 4 years! And it was many years ago. The only mistake I did is asked him for a recommendation letter for university admission. After all these years, I let myself forget his past actions at work, now this behavior is making me hate him forever. I'm feeling pissed and revengeful. I wish I could just slap him so hard his glasses fall on the floor. It was a mistake to be born in India, work for Indian manager, work for companies in India.