Dollar General review: It said it was Invalid

I bought at the Birdsboro Dollar General brought it home scratched the back for the pin number and tried to use and it said it was Invalid How can it be invalid when I scratched the silver part where the pin number is and I really wanted a Amazon gift card but there was any there we cannot go out can you email me a new card . I was charged and paid $20 dollars for a card that was invalid. My name is Darlene Emery 115 n furnace at Birdsboro, Pa 19508