I disputed a double charge and now Apple won't let me use my credit card.

My credit card company alerted me to two charges that came in very closely together, so I disputed one of them. I believe I only made one purchase but that was very little information and I can't even tell what app made the charges. Now Apple has blacklisted my one and only credit card. I have tried deleting it and re-adding and they simple say This card can't be used with iTunes. There is no way to dispute this or even report it as wrong. The card functions in person and online everywhere else. I only have one credit card Apple! Now what?