I am not sure what the BP Fulfillment means, but it looks like your order got filled. They may have found one to ship.
The initial CSR you talk to at Virgin Mobile has almost no power to do anything, and should kick you up one level about your replacement phone.
Otherwise, I do not know if they let you pick or not. My guess is that you can make a case to get something better than a phone with lower specs than the Triumph, if that is what is offered. You will have a tough time basing a replacement on the original price you paid for the Triumph.
The Reverb has a 5 mp camera with front facing camera, 1.4 ghz processor, 4" screen, Android 4.0 or higher. In my opinion, that would be fair replacement, if you can get it. You may be able to get them to give you so many dollars credit towards something better.
The bottom line is that Virgin Mobile does not want to lose a paying customer and send you to a competitor. They should be willing to work with you. Please post how it works out. Good luck!