I updated my payment method and it still says failed even when information is correct. Why does it keep saying failure?

Read the information in the Related Article above your name in the post. Your credit card holder is the one that declines a payment method, not Apple. Check with them. If they cannot answer the question, then you need to use this link to find your location and click on it to get the information to contact iTunes support. Choose your country or region - Official Apple Support