Unfortunately we are in the same boat as you
The O2 network is currently down nationally for data, with intermittent calls / texts. giffgaff is therefore affected by the same outage
O2 are doing all they can to fix it, please sit tight!
Check here regularly for the latest updates: https://community.giffgaff.com/t5/Service-Updates/2G-3G-and-4G-services-impacted-across-the-UK-6-Dec2018/td-p/22737523