For me, it was in fact a debit card. The debit card they keep asking the csv for is an old expired one. I have an iphone and I presume the info was uploaded to iTunes in the first place from my Verizon Account. However, I had swtiched Verizon to bill directly from my checking account.
On the off-chance that this would solve it, I updated my Verizon payment method to the new Debit Card from my bank. So far it has not...
I have been unable to download or update anything for a little less than a week. Still a pain, though.