I cannot install this game

Hi Assistance,

Today I bought Mass Effect 3, physical DVD copy, from a gamestore in my city.

I put CD1 in my computer and the Autorun obliges me to install ORIGIN. ok... done.

Then I am asked to install the updates. Done.

I then create my ORIGIN account, I access with my account and I finally get the window asking me to write my SERIAL NUMBER.

Unfortunately, it does not work. I tried all the procedure again and now I get this message: "this code has already been used".

Can you please help me to install this game?

Thanks!

Carlo