Agents do try to help whenever possible and they do frequently refund in situations like this.
But did the agent explain why it happened and how to ensure that it doesn't happen in future? I'm not sure they always have the time to do that.
My reason for asking is that you describe the problem as
yinku13 giffgaff double debited my account
It's unlikely that giffgaff debited the account twice for the same transaction. More likely is that there were two transactions -- one which bought PAYG credit and one which bought a goodybag. Two separate purchases, not two charges for the same transaction.
It's not a good idea to try to buy goodybags that way because the phone can (and often will) use some of the credit before you have time to buy the goodybag. So, by then the remaining credit is less than the cost of the goodybag and it has to be bought as a second transaction.
So, here's a guide to buying goodybags safely:
If paying by voucher:
- make sure you buy a single voucher, which can be for either giffgaff or o2. Do not allow the store to sell you two vouchers totalling the price of your intended goodybag
- either dial 43430 and choose option 2 not option 1 then listen for the option to buy a goodybag from a voucher
- or go to https://www.giffgaff.com/buy/goodybag and make sure you choose the option to pay by voucher
If paying by card or paypal
All of these options buy the goodybag without ever adding PAYG credit, and therefore the situation you describe cannot arise.