en0093 Right. You are right o2 vouchers work on giffgaff and you thought right as there is a £50 value o2 vouchers.
You haven’t done anything wrong here as o2 vouchers range from £10 to £50 according to this https://www.o2.co.uk/topup
I wasn’t aware giffgaff systems wouldn’t take that value voucher albeit being a valid one.
Are you redeemed the voucher online here http://giffgaff.com/buy/redeem or through the 43430 line from your phone? Try both
Otherwise contact the agents about this using https://support2.giffgaff.com/app/ask/Top-up-balances-and-goodybags/Using-a-top-up-voucher/form/
They will respond within 24hrs
Check for reply from agents using link below
Please let us know how this is resolved
All the best