Question about Vanilla Visa prepaid credit cards.

So for the steam sale, I bought one of those prepaid CC's. I bought a 75$ Visa one. I added 50$ to my steam account right away, kept the 25 in it. Fast forward to today, I've spent about 10$ of that 25, yet I try and buy a 5$ game and it declines it. So I go to vanillavisa.com to check out my balance, and when I log in with the card info, I get this error message: 'Details could not be found using the card number entered. Please re-enter correctly.'. I am positive I've entered everything correctly. Anyone know what's up?