Out of interest did you set up your phone to use giffgaff data?
If not you can use this app to helphttps://play.google.com/store/search?q=tweakker+ics+apn+beta&c=apps
You'll need to run the app and follow the instructions.
Or you can do it manually
System Settings>Wireless & Networks>Mobile Networks>Access Point Names
MMS proxy: 184.108.40.206
MMS port: 8080
APN type: not set
Leave any other fields at the way they are.
Make sure you save your settings
Make sure your new APN is selected
If there's an option to select "use packet data" make sure this is selected.