Hi this might help and confirm network issues Giffgaff network status I suggest you check the network signal status in your area to see if you’re having any outages or if any maintenance is being carried out by entering your postcode here http://www.bit.ly/ggservicestatus plus
Please remember that the Website is updated hourly and may Not show any issues at the moment , also try Turning your Airplane Mode ON and OFF again and see if that helps. If the Signal Checker is showing NO reported issues, Please try performing a manual roaming usually that sloves majority of text problems please check out this guide https://community.giffgaff.com/t5/Tips-Guides/Manual-Roam/td-p/3345471 on how to perform a manual roam.
And try turning your device off again for a couple of minutes and then turn it back to force the device to refresh the network signal. If after doing the above you find it's still the same then this thread could be worth a read too