I became an obsessive FB marketplace user buying up tons of other peoples old junk until one day I initially offered to purchase a table but discovered that IKEA was selling the same table for 5$ less in new condition. I explained my reasoning to the seller and sent her the link and within minutes I was banned from Marketplace with no recourse. I don't know if she reported me or something.

I was really bummed for weeks because FB support does not exist. But after a while I figured out that if you sign up for FB verified you gain access to human based support. I did so and eventually they managed to restore my account with no reason as to why I was banned. Maybe that will help?

I don't have a solution, but I tried to do something similar and asked my friend who is a manager in data and identity management at Facebook how I could create an account for some experimentation. He explained to me that they are very strict on identification nowadays and the only way to get back into a locked out account is to show ID next to your face on camera.