I had this problem. Here's my issue (and I think, fix).

I originally entered the pre-order code way back when, and it gave me another code that I wrote down in a text file. I totally forgot about that file. But (on pc at least) you're given a second code after entering the first. I was able to find it again hanging out on a .txt file I'd sent to my recycle bin. But /that's/ the code you have to enter in mog station. It's really pretty horrible design and implementation on SE's part... but if you can track that code down and enter it in mog station, you should be able to get your early access.