Have you made any calls to Calls to international numbers or 070(call-forwarding services), 084, 087, 09 , 118 mobile numbers? As these calls are chargeable from airtime credit and not included in goodybag allowances.
The goodybag allowances only cover UK numbers that start with 01, 02, 03, and UK mobiles starting with 071 to 075 and 077 to 079. It is free to call numbers that begin with 0800 and 0808.
A list of Inclusive and non Inclusive call, texts and services can be found here https://giffgaff.com/support/questions