Give me your credit card number and I'll try putting it in j/k
Seriously though i had the same issue when i changed my credit card and had to add it to my XBox Live account...not sure what the issue ended up being but I called up support and they put it through for me.
Call Zune support or contact @zunesupport on Twitter. Both are very helpful. I had a similar issue when trying to add my credit card for Zune Pass and had to call Zune support. They were very helpful and resolved the issue quickly.