The quickest way to resolve this is to call Samsung Support on 0330 726 7864
They will direct you to the nearest Samsung centre who will repair the phone on the spot. Far far quicked than returning a new phone to giffgaff.
Sorry, just read that it was refurbished.
I would still take it into a Samsung Centre as giffgaff have a nasty habit of categorising any cosmetic problems as 'user damage' and charging accordingly.