Terribly sorry that you have not received your cheque yet. I'll try and find out what I can but in the mean time could you check what address we hold for you here - https://www.giffgaff.com/profile/details#address
I don't have access to your account and it might be best to contact the agents about this as they would know better than I if this cheque has been sent to you.
Can you make contact with us on this email - email@example.com
Just wondering when refunds as credit will be issued and how much many thanks