In Halo 3 your katana and security helmet disappeared and you have almost 1100 gamer score for Halo 3 how do you get them back?

this happened to me when i got the triple kill acheivement at 1005 it seems when your gamer score goes up you lose it and then you have to get three more achievements to get it back ...... vidmasters don't seem to affect it i got 7 on 7 monday didnt go away so..... my score is now 1125 47 achievements