Hello there, I’m living overseas, I bought an ATT iPhone XS Max from a seller on Offerup, he told me the cell was factory unlocked. When I get it, I realized it wasn’t. I contacted the seller, he never answered. I tried to get it factory unlocked by a third party, they say the cell is still in contract and has been blocked by ATT. What should I do in this situation? How can ATT help me???