Can you check if you're actually using airtime credit and not a goodybag?
Dial *100*7# on your device. Does it say you have minutes remaining? If not, you are using auto top-up, not a goodybag recur.
Buy a goodybag here: https://giffgaff.com/profile/payment-details#autosettings
If you still need help, feel free to reply to my message and mention me by adding "@mrjeeves" to your message.