When you make a payment that is returned, AMEX will immediately freeze all cards associated with your social security number. Frankly, I think this action is a bit excessive, especially if you aren't past due or still had credit available unrelated to this payment, but it is what happens.

If the payment was returned for NSF, it will be represented to your bank twice more. Should it clear, it is treated almost as if this never happened for any recourse actions or future credit decisions (though sometimes they will assess a fee). If after the third attempt the payment is still returned, it is noted on your account as a returned payment and will certainly impact you for up to six months if you try to get more credit with them or make any large payments (they will not immediately be available to use). Any more than a few of these "final returns" and they may actually cancel your account.

In your case, a call to the account services department (customer service will connect you to them) should be able to clear this up. If the payment has cleared your bank, just inform the rep that and they will have a conference call with you + your bank to verify the payment has cleared, then they will immediately clear the hold off your cards. Should you not call them the hold will stay for an additional 5-7 business days.