I'm not being sarcastic in saying this but have you double checked you're not misreading letters for numbers and vice versa? Sometimes the font used doesn't clearly discriminate between the two.

Each code should consist of five sets of four characters. Mine happens to be mainly letters with fewer numbers. It should look like this:

ABCD EFGH IJKL MNOP QRST

Any character can be a letter or a number, so that's not something to worry about. There's 20 characters per code in total.

The code needs to be put in your account on the Mogstation under "Bonus Items Codes". Are you sure you're putting it in the right place as I seem to recall from earlier codes that there are numerous places on the site that mislead you!