Delta airline cargo overcharge for cargo, Internet

On February 10, 2010 my cargo from Moscow arrived to Atlanta. It was carried by Delta Airlines in Atlanta Hartsfield airport. My assistant,after the cargo was cleared from customs, came to Delta Cargo office to pick up the cargo. Upon arriving she was told by employee of Delta that the the  Air Way Bill was lost by Delta, so they will print a new one from their system. They printed the new AWB. And ask my assistant to pay 2074$$. So she did.

 When I came back to my office 2 weeks later I look at the copy of my original copy of AWB which was sent to me by mu customs broker   , I find that this game with"lost" AWB cost me extra 1100$. Delta simply overcharge my assistant 1100$ claiming they lost the documents and charging her $5.50 per kilo instead of my original rate of 2.05$

 Next day I call to Delta with  complain ,they told me that I have to e-mail to accounting department about this matter. I submitted all evidence to them and 3 weeks later i still recieving e-mail from delta asking about same paperwork which was already sent. I also visit "Delta Cargo Office international " and spoke with manager Natasha  she told me that it was Delta mistake and she will take care of this. nothing happened. Now I am thinking to hire a lawer and sue them for unfair business practice..

Is anybody had same expierence?? It looks like they didn't do it a single time. 2 weeks later when I personally pick up next cargo, Delta clerk started to play "lost documents" game with me but I showed him a copy of mine and he accept the rate of 2.05$