I was in the same boat as everyone here this morning. I tried all the suggestions: re-redeeming, setting language, filling out profile, etc.

My suggestion (it worked for me!), although it's a painful one, is:
1) Open support ticket at support.na.square-enix.com.
** Provide your 6-3-6-3 code and your broken 20 digit code
2) Call US support center 1-858-790-7529 (during business hours!!)
3) WAIT! I was on hold for just under THREE (3) hours!
4) Give the tech who answers your ticket number, calmly and politely explain the problem, and answer any questions they have.
** I was asked where I preordered from, what URL the retailer told me to redeem at, what my 6-3-6-3 code was, what my incorrect region 20 digit code was, etc.
5) Tech will give you a new code (hopefully?) and wait on the phone while you enter it
6) Say "thank you!" and hang up; then relax until Saturday!