I'm in the exact same situation but only have the Aspire. Have you been making transactions on your Aus card? Reason I ask is I got the Aspire a few years back and have changed passports since then so a different number so unless they only use the name and birthday for reference, I'm guessing US Amex wouldn't be able to link the application to my current US account?
Which makes me wonder if they are looking at spend on the Aus card instead?
Do you mind me asking how much you are spending on your US cards? I'm only really using the Aspire when I stay or eat at Hilton and using their annual certificate so I'm clearly in the unprofitable category for them.