IPhone bought on eBay is replaced at Apple

I purchased an used iPhone 3GS 32GB off eBay India in October. The phone was running on a jailbroken ios 5.1.1. In my eagerness to use ios6 just as Apple intended for users without jailbreaks, I requested AT&T to unlock the device through their website. Initially, the request was turned down over e-mails. After which, I decided to call them. A few persistent calls later, I was directed to the supervisor who told me that she will place a request with Apple and that I should restore my phone after 48hours to effect the unlock. Happy with the conversation, I restored my fully functional device on my MAC using iTunes. iTunes downloaded ios6 to restore the iPhone. After the restore, my iPhone just connects to the iTunes server requesting activation. I get an error message stating "the iphone activation has failed due to a server error and that I should try later." Many trys later, I decided to verify the serial no. with Apple's support website. To my surprise, Apple says that the device has been replaced and that I should present it with a valid serial no. Now, I am stuck with a bricked iPhone and don't know who to turn to. Please help. A few points that have come to my notice: the SSH blobs of the iPhone until 5.1.1 have been saved at Cydia and I am unsure of the baseband of the phone at the moment. I request for someone to guide me tide the issue. Thanks in advance. Any help from the community will be appreciated.