error payment validation

I am facing a problem with my apple id. When i sign in in the appstore on my iphone or itunes on pc, it automatically sends me to a page to verify my payment method. It declines to accept the payment information i have always been using (there is a billing problem with a previous purchase. Please update your payment method). it then says your account was changed while you were editing your account information. we were unable to save the changes. Even if i put a new card number and details it says it cant be used. It doesnt give me a 'none'option either.I only want to update the apps on my phone which are mostly free but fail to do so. Its really frustrating since some of the apps like whatsapp keep on crashing after updating to ios 8. I searched online and the solution is to update the app.

Iphone 5s, ios 8.0