eracode:andrewNZ: If I read correctly, the main question here is "does a refund count towards my 'minimum amount to pay' at billing time"
I suspect the answer is no, although it will reduce it proportionally due to the reduction in outstanding balance.
The refund credit will count towards reducing the full and the minimum amounts to pay (from what they would otherwise have been without the credit) in the current month if the credit has been processed in the current month.
If it is processed after the cutoff date, it will reduce the full and minimum amounts in the month it is processed.
Bingo! That's right - according to the bank.