Go in to your settings and go to browser profiles and make sure the profile selected is your GiffGaff internet settings. If its not there then you need to get the settings from GiffGaff and install them, you can get the settings by texting "settings" to 2020 hopefully that will work for you
I had a similar problem on my phone which is a nokia slide. I found that because I'd had it unlocked I couldn't access the Internet through Home as it was still set to my old 3 settings. Instead I manually type the web address in and that works fine. Try it with yours it might help.
This is what i did to my samsung chat ch@t 335 to get my internet working.
Text settings to 2020.
you will recieve the internet settings shortly.
Then go to internet, click options and go to settings. Edit the giffgaff settings and change the port to 8080. it should now work
Help please Internet not working:/ texted 2020 and 1010 dosent work
Try this guide:
I have the same phone
To fix the problem i manaually enterd the gifffgaff interent into my phone by createing my own "using the guides given above"
then i made sure that the internet profile was set to giffgaff and then it started to work same with MMS