Credit Card Validation

I’ve completely lost access to my account because each time I log in it insists that my credit card is invalid. I’ve followed the steps to re-validate with three different cards from three different banks, and when I complete the validation it shows it’s been approved, but then I go back to the home page and it’s still showing as invalid!

I’ve lost count of how many times I’ve emailed Amazon Seller Support and been told to re-validate the card, and I’m now at a total loss as to what to do next.

What’s most frustrating is that all I want to do is close the account, so why it’s insisting on this credit card validation is a complete mystery to me.

Does anyone have any advice on what else to try, or maybe the details of how to raise a formal complaint to get this escalated please?