If you've been given an Xbox One code instead of a PC one; follow these steps:
On EA Help - Search for Titanfall and select Contact Us.
Select PC as the Platform, and click Next Select the Topic - Demo/Beta and type in Eligibility Issue in the subject line, and click Next Click on Email Me. On the next screen, when asking for What type of Demo/Beta issue you are having, select Eligibility Enter the Titanfall Beta code that is not working as the description of the problem. Select Submit. You will receive a new PC code within the next two hours.