Sounds like you have your goodybag set to recur so you need to switch that off.
How to cancel your recurring goodybag
Go to: https://giffgaff.com/profile/payment-details
Untick the "Recur your selected goodybag" box and click on "Save recurring settings".
Go back to "My giffgaff" https://giffgaff.com/dashboard
and you'll see that your recurring goodybag has been replaced by the following message " You can switch your goodybag to automatically recur every month".
That's it, your recurring goodybag has been canceled. You'll be able to select a new recurring goodybag by clicking on the "recur" link. https://giffgaff.com/profile/payment-details#goodybagsettings
If you ask an agent they might be able to refund you for the goodybag payment that you didn't use.
You can contact an agent by sending a message from this link: https://giffgaff.com/support/ask