FNB and ITunes wont update my payment information

I received an e-mail from ITunes informing me that there was a billing problem with my membership subscription and they could not process a payment. I tried to update my payment information using my latest card and ITunes keeps on saying it is not valid. When I called FNB, the bank said that they could see that the payment was declined but on their side everything is normal. That is, my account has funds and my card is active and updated for digital and on line purchases.

FNB said they could not do anything on their side as Itunes is a 3rd party site. I must call Itunes. I call Itunes and they tell me that I need to call my FNB and ask them to authorise the payments and then I'll be able to update my payment information.

I call FNB and they tell me that they cannot authorise the payment because Itunes needs to call them to authorise the payment stating the payment number. I call ITunes and I am told that ITunes cannot call FNB. What exactly am I supposed to do. I have not received any assistance since 08h30 this morning.