Hi @jimmycheen, complete a Soft Reset this will resolve any Internet APN issues.
Press & Hold the Volume Down+Power buttons for about 10 seconds until the screen goes blank and the phone vibrates. Also ensure Mobile Data connection is ON, and Flight Mode is OFF.
Try visiting giffgaff.com on the phone to ensure it's connected. If you can visit GiffGaff but no other website, then you haven't got an active goodybag nor airtime credit (for PAYG)