@shang66 Hi Shang, I think you are confusing goodybag allowance and airtime credit.
With giffgaff you have to purchase your goodybag it is not automatically done by adding credit to your account.
Goodybag allowances last a calendar month from purchase so if you did purchase a goodybag dial 43430 and select option 2 and listen to the recording and if you have a goodybag you will hear the amount of allowance remaining and the expiry date.
For the future if you want to purchase your goodybag using a voucher (or from credit) use the phone line by again dialling 43430 and selecting option 2 and then follow the instructions for the goodybag you want
If you are using a bank /credit card or PayPal you have to do it online using this link
It is worth noting that you can not purchase a goodybag every night between 9pm or 10pm online until midnight (some nights later) because the giffgaff goodybag system is busy recurring the days new goodybags