Cannot pull more than the most recent billing period.

[nm523]

Working code example using the examples/amex_to_pandas.py script, and passing in a billing
period greater than 1.

This might just be an issue on Amex's side, but we'll have to see.

Error message:
`

<XMLResponse>
    <ServiceResponse>
        <Status>fail</Status>
        <Message>Our System is not responding. Please try after sometime or call Customer Service.</Message>
        <MessageCode>0005</MessageCode>
    </ServiceResponse>
</XMLResponse>`