You can either get a refund back or keep it on your account for the next time,
If you do want a refund, >>
If you want a refund back,contact a agent and fully explain to them, if your purchase was done by a Credit or Debit Card make sure you have your bank details stored so that they can refund it back to your bank, please allow up to 3-5 days to receive the payment back to your bank.
The Agents >
⬜ Contact a agent : ➜ https://giffgaff.com/support/questions
● Also : Please be patient, the response may take up to 24 - 48 hours for a agent to reply