lost xbox live card

Sorry to hear that you had to pay twice for your grandson's gift but according to the Microsoft gift card terms and conditions
Microsoft isn't responsible if your gift card is lost, stolen, misplaced, or used without your permission.

Please see section 2.2 of the link below.

https://support.microsoft.com/en-us/help/10562/microsoft-account-gift-card-terms-and-conditions

if you have the card in hand then it may be possible to recover the code, you need to talk to support, but having a refund will depend on where you bought it and store policy

Hi There,

It depends where you bought the code from and what their return policy is. Sometimes digital code sales are final and sometimes stores have a way to check if the code is still valid or not, so it depends. I would just bring it back to where you bought it
and try your luck.

if the code is on the receipt you can type it in with that but Microsoft cards are nonrefundable

Im going to say it’s unlikely that you can get a refund because they would have to deactivite the card for them to even try to refund that. I know for me they don’t do refunds they even tell you that before you hand over the money.