PIN NUMBER

Ok, I have two new itunes gift cards and I'm trying to use them. But I'm having a problem with putting them on my account. I go store and sign in, then click prepaid cards. It says to enter the card number and pin number. First, I couldn't find the pin number and then when I finally thought I got it and pressed enter. It took a couple minutes to check it and then said "We're sorry. Our systems are unavailable at this time. To check your balance please call the toll-free number on the back of the card." So I checked on the back of the card and there was no number. So I tried an hour later to see if there systems weren't as busy and they were. I don't no what to do.

Windows XP