Around Christmas time, I gave a family member a pre-paid card for their 3DS and recently they decided to redeem it. When scratching it though, they didn't take the wisdom of the card into mind and scratched it with a letter opener, ruining the midsection of the code so only a few numbers and letters are identifiable. Would I need to call Nintendo to help sort this out and would they even be able to help?
No worries. Give Nintendo a call at 1-800-255-3700 (open 6am to 7pm, 7 days a week), or e-mail them using their webform, and they will likely ask for you to send in the pre-paid card to them and they will then credit your Eshop account with the points.
The same thing happend to me too. I called Nintendo at 1-800-255-3700 and they told me I could fax or e-mail a picture of the card. In a few days, I got an e-mail saying that the $20 is now in my account.