Depending where you purchased your vouchers they can take up to 24 hours to become valid. Check and see if they are represented in the voucher catalogue it can give you some insight into your vouchers. If they are not represented please consider adding them after you have successfully loaded them onto your account.
You can also try it using the 611 service. Make sure you're using the right set of 12 digits if you have more than one. It's silly how they print these things out.
