My card is unreadable and it doesn't start with any of the numbers or letters above? I need to purchase a book for school. Please help me.

I have for the past three and a half hours have been trying to redeem my itunes gift card. It is for $25.00 and I need to purchase a book. My card is unreadable....The first letters and numbers are fine but the middle....looks like four numbers/letters combination is missing and then the last four digits are fine. I have typed in what looks just like the letters and it says invalid everytime. So I went to express and did what they said and still it says invalid. I don't want to throw 25.00 dollars down the drain. Can anyone tell me how to fix this problem?