Once an IMEI has been blacklisted, then the phone is rendered useless. If you bought it from EBay or a similar service, contact Support and immediately request a refund along with the statement from the carrier in which they tell you the phone has been reported stolen. They should grant a refund. Make sure to leave negative feedback on purchase to send a warning to other users as well.
You can visit a local phone shop to see if they can revive the phone and generate an IMEI based on the old one. This is the only chance, but it will also cost you.