Please make sure your Airport Extreme is not configured in bridge mode as DNS changes will not work. If it is configured in bridge mode you cab either set DNS on your main router or remove bridge mode.
- Open Airport Utility which you can find in Applications > Utilities
- Select the Airport Extreme from the menu and click edit.
- Fill DNS server fields with these values:
- Click on Update.
First step of troubleshooting should always be to restart device(s) and router. Then check your account status in your account. You should always see 3 green check marks if the device you are using to visit the account home is set up correctly.