So I recently bought an iPhone 12 off of FaceBook MarketPlace and I was looking up the IMEI number and it said it was Blacklisted and I can't get in contact with the person that sold it to me I don't know what to do now.
If you can't contact the seller for a refund and Facebook isn't willing to help you either, then you're out of luck. The only person who can remove a blacklist is the original owner, who is most likely not the seller either.