why cant i add my card to my appleid which was working

Suddenly this morning my applied on my phone asked me to sign into my account which was fine, I did so. However my valid card was coming up as invalid with “payment method declined” as the message. I am almost positive that it’s not a card issue as apple wallet accepted my card just fine and I have been able to make online purchases. I can’t even update apps onto my phone because every time I try to I have to sign in but I can’t complete the sign in without a valid card! Please help