Unable to add credit card payment method

When I submit the payment method form, green message says payment method was added, then another message says there are no payment methods and loads the form again. I tried from laptop and iPhone - same experience. Credit card is Amex issued and address in USA - no problems using anywhere else. Contacted support billing@ - no reply in 3 weeks. Case 01329481.
This is my last ditch effort in case anyone has had a similar problem and has figured out a trick, or in case anyone happens to be listening.
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