to confirm the status of the device and which carrier initiated the block. Are you the original owner of the device, or was it purchased from a third-party seller Check the IMEI status of your mobile device - AMTA

An IMEI (International Mobile Equipment Identity) is a unique identifier for a mobile device. When a phone is reported lost, stolen, or involved in fraud, carriers or authorities can add its IMEI to a central blacklist/database so networks block it. "IMEI blacklist removal" refers to restoring a device’s ability to connect to cellular networks by removing it from such lists.