Um... how did this happen in the first place?
Were you buying many cards? Took up 3 and activated 2?
Scanned same card twice?
Why were you holding onto it for a week?!?!
call the store, hopefully they have it on video.
Morals of story:
Don't buy cards you are not ready to load.
Check the receipt to match the cards to receipt
LOAD ASAP.