Every time I try to update or add a app it prompts me saying I have a purchase that was declined and I need to add new credit card or put my 3 digit credit card on file security code. The problem is I have not purchased anything thru App Store.

I have a iPad and every time I try to update or download a new app from the App Store it says I have a declined purchase that I need to handle first before updating or adding anymore apps from store. I am then told to enter a new credit card on file or put in the 3 digit security code I have for credit card on file. I very rarely purchase apps. I typically only download free apps from the App Store. How can I figure out what they think I purchased and cancel it so my App Store will work properly again??