won't let me install free apps

I have an iPod touch IOS 8.1.3, my problem is that just a few days ago I could install free apps well all of sudden starting today it asks me to put my ccv code from my credit card, says there's a problem with a previous purchase, well I do that even though it's a free app and it says I need to update my account well it's a pre-paid card so I don't have any $ on it at the time which is why I was downloading a free app, so I thought that maybe something was wrong with that app so I tried downloading just the flashlight app, same problem goes straight to asking me my ccv code on the back of my credit card, pls, pls help me, that iPod is pretty pricey and I've only had it since Christmas, pls help me fix...Thank you