Blacklisted iPhone

Is there anyone who had a luck removing an iPhone from blacklist through ATTCares or at least get notable help?

Before posting it here I have sent 3 PM’s to ATTCares(about heir own interest). No response so far.
Recently I have purchased a brand new sealed in the box iPhone. It was not blacklisted at the time of purchase and for the following couple of weeks it showed status as clean. Then I found out that it was blacklisted. I have a proof that I purchased it from an individual. Seller also showed the IMEI. Apple database shows the phone as a valid purchase.
I can’t post the whole story here (its too long) but my understanding is that it is an insurance fraud. I tried to talk to ATT customer service and get more information. The only information I got was this phone is deactivated. Nothing else. They don’t even want to provide me the reason. I don’t want to go to the police without knowing the reason for the block. They have more important stuff to do.
Of course Seller is ignoring me now. Im not pushing him for now.
Luckily my state has a law that protects consumers. But it is a long process.