Device unlock

Hello! did not buy an ebay LG g5 h820, IMAI [edited for privacy – please do not post personal information]. The seller in the description indicated how clean the IMAI was, tried to untie it from the operator at https://www.att.com/deviceunlock/#/, your service reported that "the phone is stolen / lost " ...What should I do? I'm not from the US and I do not have a contract. Help me please!