Banggood is well known and respected for providing really sharp customer service, especially here to members on the forum, but it seems to have been really disjointed throughout this entire process for you unfortunately and not effective at all. That said, the issue itself can be laid at the feet of the scammer and of eBay who played their part in allowing the scammer to get away with it to start with.
So Banggood were really in a position where they couldn't do a lot, but they certainly should have been more helpful than just simply requesting the same info over and over again. Better customer record keeping is something that should be high on the to do list it would seem.
Scammers screw the whole market up for everyone, I'm just not sure what the options are. Something we all have to live with, just have to protect ourselves as sellers as much as possible.