On further research, it seems I don't qualify for a merchant account since I am outside the US. But if they cannot provide me a merchant account, at least they should send back the payment to my client, so that I can receive it another way.
But they have terminated my account, are refusing to talk to me, and have also refused to send the money back to my client.
At this point I would like to know if there's a way to contact a higher-up at QuickBooks, or I have to file a claim in small claim court to recover my money.
You could have your client initiate a charge back through their credit card company or refund through their bank depending on how they paid.