users bypassing IP ban

I store in the DB a list of "bad" IPs, and in my controller for the sign up page I redirect users whose IP is found in the list of bad IPs using this code:

Code:

redirect(base_url('xxx'));

But a user was able to bypass it and register with a blocked IP. How is this possible? Even if the HTTP redirect could somehow be ignored, the "redirect" function terminates script execution (as explained here)

I'm using CI 3.0.4 is that helps.