So before you ordered, GB had the product, and you had the money.
You made a deal that you get the product, and GB gets the money.
And now, GB has the product (again), and they also have your money.

In simple terms: the seller is responsible for the product until the buyer has it in his/her hands.
GB admits that the product is (again) in their posession, through no act or circumstance on your side.
So it is fair that they fulfill their obligations, because you did fulfill your end of the deal.

GB has two options: fulfill the original deal, and send you the product (you have payed for already).
Or reverse the deal and return (all) the money to you.

I am sursprised that in everything GB proposes, a 3rd party (who f* up) still gets his/her money.