PROBLEM RESOLVED

So this was my problem:


I had to dig back into my emails, to retrieve that old email that sent me the Shadowbringer Pre-Order activation code.
I clicked that red button that says "CLICK HERE TO GET ACCESS TO YOUR PRODUCTS".
It brought me to the page which I got my Pre-Order activation code. But now a new button appeared that for me to retrieve the REAL Shadowbringer activation code.

After that, I logged into Mog Station, pressed "YOUR ACCOUNT", and then just entered the code in there.

Problem fully resolved!