I've not gone through the process of asking for an increased credit line with Amex before, so my experience may be of little utility for you; however, with both Chase and Citi, I just called up and asked for an increased credit limit. In both cases, I was sent to a separate department who verified my income with me and approved the increase over the phone. In both instances I was also asked why I wanted the increase, which, I explained, was to not allow my monthly utilization to each more than 30% of my available credit on the card (i.e. it wasn't so I could max out my newly increased credit).

I'd suggest trying again, and if that doesn't work, perhaps try asking to speak with a supervisor so that you can find out if Amex does have a "live" way to process credit increase requests.

But if you do find the answer, be sure to post what you find. A lot has changed recently with CC issuers. From my experience Citi is completely unwilling to reallocate or combine credit lines, whereas in the past such requests were always honored. Others may have had different experiences. I've had similar experiences with Chase, except they do seem willing to reallocate lines when applying for a NEW credit card account. Good luck!