You will need to speak to a giffgaff agent regarding any account issues as well as processing any refunds, as they are the only ones that can access your account and help you with that.
To contact the giffgaff agent use this link: https://support2.giffgaff.com/app/ask/Top-up-balances-and-goodybags/Credit-debit-card-or-PayPal-over...
The agent will try to get back to you as soon as possible, however, during busy periods the agent can take up to 24 hours to answer your question.
Agent replies can be found here: https://giffgaff.com/support/questions
Hope this helps,