I was unable to load my voucher.

Most of the people on these public forums, including myself, are fellow users - you're not talking to iTunes Support here. I've asked the hosts to remove the card number from your post, hopefully nobody else will have read it and been able to redeem it.

Was the iTunes card issued in the same country as your account is based (they are only valid in their country of issue) ? If it was and the page that you posted from doesn't help then you will need to try contacting iTunes Support (you will probably need to give them images of the front and back of the card, and possibly its receipt) : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then iTunes Cards And Codes