I had the exact same problem last week. (there:s a post about it somewhere) They told me there had been a billing glitch so I wasn:t billed for the second month, had to cancel then resubscribe.
Not good for my heart--it happened right after I was approved for my first amex and then I couldn:t see my reports!!!
I was worried about the same thing that angiepharm mentioned, being double-billed, but haven:t seen anything yet.
And their customer service? painful. seriously. I hope there:s not a problem because I:d rather pay double than go through that again.