My black ops 3 code isn't working (invalid)

Hey there,

I recently pre-ordered black ops 3, and received my code for beta, but when I input the code into the website it says its an invalid code. What do I do? I've tried going into the Black Ops 3 Beta FAQ but when I click my problem it just brings me back to the same page.

I don't know what to do?

Thanks,

Protom.