Thanks for the info.
I think it would be good to start by updating the OS. A new version was announced a couple of days ago.
It may take a few days for your operator giffgaff to pass it on. You can check by going to
Settings > System > Advanced > System update.
Once that’s done you may see changes in the Mobile network settings.
On the subject of APN can you check that the current values are as specified here
There should be a second APN record for MMS as specified here.