How do I resolve this?

I have an open order ‘awaiting payment verification’ from 6 months ago.

To fix this, I think you should get in touch with Amazon Seller Support to check the payment verification status of the order and ask for assistance in resolving the issue or canceling the transaction. If you have any further questions, feel free to reach out.

Six months? Wow… I would open a case, mate, and see what’s going on.