Here are the manual settings to input if the 2020 text doesn't work You'll need to go to Settings General
Mobile data (or celular or celular data or network) Mobile(or celular) data network (scroll down if not visible)
It Should be like this, if not change it.
GiffGaff don't currently support this, so leave it blank
MMS proxy: 126.96.36.199:8080
MMS Max Message Size: 2097152
MMS UA Prof URL: leave this blank
Please be aware that MMS cost 16p and are NOT included in ANY goodybags