PE from old firm wont verify my experience. Has tried to sabotage my career previously and sent nastygrams to my current employer in past

I am a female engineer and immigrant on H1b visa. When I graduated, I couldn't find companies that would sponsor my visa. After sending resumes out to companies in DC, VA and MD area, Firm A started me at low wages (below the requirement for engineer salary acc to US labor dept); I was on STEM opt at the time, and accepted it because I just wanted to gain experience. I was treated terribly at this firm, not to mention being the only woman. I would hear comments from my boss like "Why cant you marry someone, so we wouldn't have to keep paying for your visa".
Note this is a small firm - 10 people (only 2 PEs who were also principals at company, and no HR dept- My boss was HR, accounting etc) I got 1 week of vacation and worked 60 hours for low pay. I thought this was normal, as I didn't know any better, and have no one in this country (family). My friends were sympathetic and supportive, which helped me get through.

This was during COVID times. Also not to mention, he made us come in Washington DC office and said we dont need to wear masks or practice social distancing because covid wasnt real. I was scared for my life every day for months. It made my mother ,who lives in my home country, cry many times fearing for me. As you all know, it was a scary time when we didnt understand COVID-19, my roommate hated me and blamed her grandmother's death on me, because unlike her I went to work and exposed her to it. Anyways, I just had the worst life at home and at work then. This led me to find a new job.
When I finally gave me 2 week notice, my employer insulted me horrifically. I quote "I picked you from the street and gave you a job, and this is how you treat me?! you will never succeed, I'll make sure of that"
Note that I had my EIT at the time, and have a 4 year degree and I sent my resume out to firms back then. So none of what he said was true - except for the last part which he seemed vindictive enough to do.
I had worked at Firm A for 2.7 years then.

After joining my new company Firm B, I have been promoted 3 times (in past 3 years), I love it here. They treat me well, and I have learned everything from chiller design and FA system design.
During my 1 year review, my new employer had great things to say about my performance and mentioned (while laughing) that my old employer had sent them several emails AND letters saying disparaging things about me. He didn't say what exactly, but said that he sounded so vindictive, and unprofessional and that they dont care. (Thank goD!!)

Then I needed my public trust clearance for my Firm B jobs - and background investigator called me in for interview and I had to tell him the full story about my old employer. He said my old employer denied that I worked for him as an engineer. I was shocked. He said a number of bad things, and that I had to prove otherwise. Thankfully, I had STEM OPT papers (signed at the time by ex boss), H1b petitions, pay stubs, some emails, offer letters, and client and employee references! I also had a good character reference FROM my old boss signed of back then! The US office of personnel ruled in my favor - I got my Clearance!!

Finally, coming to my present issue - I'm writing my PE exam (hvac) and I've been with current company for 3 years. I need 4 years to write it. I am willing to go to VA, MD or NY as well, but they all have same requirements. after several phone calls, emails - calls from Firm B HR person - my old boss says he will do it but never does. This is his vindictive game. He wont sign off on my experience!
What can I do in this case?
I am willing to complain to board about unprofessional conduct.
Thanks for reading this semi rant, semi-cry for help. any help is appreciated

You should write a letter to the PE board in which the supervisor is licensed and explain the situation. They may view this as unethical behavior to prevent the licensure of another engineer.

You should document the harassment and submit it to the PE board where this vindictive boss is licensed so he can learn a lesson.

Thanks for sharing your experience with us. This is horrible and I feel terribly sorry you had to deal with that!

Given that the original post was made a few months ago, I hope you got the situation resolved. If not, I think there would be a way to get around that by writing a cover letter to whatever state engineering board explaining the situation (similar to what you have put together in your post) supporting it with the ruling of the US office of personnel. Since the US office of personnel rules in your favor, I believe you have a very strong case to present to any engineering board to document your 2.7 years of experience.

As other colleagues indicated above, it would be a good idea to report that person to the board where he is licensed so that the board can actually role in your favor and whatever winning decision you get will definitely serve you well in the future getting licensed in other jurisdictions. Maybe the board will force them in a way or another to sign off your experience. If that happens, I recommend you to have them signing off the experience documented as part of your NCEES record so that you won't need them again in the future (as the NCEES record is recognized in all states in-lieu of individual experience forms).

Good luck - and if possible, please keep us informed with how it went so that other colleagues can learn and understand what their options are when they run into such an unfortunate situation/employer.

All the best!

Company A's name and the principles' names please. If we do not reveal them, they just keep doing these evil things to others again and again.