I cant get the Treasure hunter achievement in Final Fantasy XIII! Please help!?

I finally have gotten every accessory and every weapon in the game, and when I go Bhatki to unlock the achievement he tells me, "Bhatkis bonus byte 5" I don't understand! I have checked, and made sure that I have every weapon and accessory! The only thing I could think of is that when I go to Bhatki, I only have a few accessories and weapons, because I literally sold them right before I went to him to get four dark matters for the last things I need to upgrade. But I was told as long as you had everything at one point you are good, and I have! I have the checklist to even make sure! So could someone tell me something I could do! Please!?