I just tried this and it DID NOT work!!!
You will not be able to enter "please cancel Amex card ending in 0000" because the subject line only allow 36 characters (yes, I counted). You would think that advances in information technology would allow subject lines longer than 36 characters, but no. If you even try to type in the 37th character, you'd see that the pre-filled email field would get over-written by your 37th character because the geniuses at Citi thought it would be a good idea to automatically focus on the next text field once you have typed in 36 characters.</rant>
Other than this, this method seems to work. Thanks sdsearch
You are making it way more complicated than it is.
Once you pull up the targeted card, all you need to do is to click on the
Email Customer Service on the left side of the screen and it would bring up the SM screen.
Choose the Account - Other
Type in Subject line something like Close Account ending XXXX
Type in the body of SM that you want to close whatever account ending XXXX.
I always add a greeting and a thank you after the request.
Within a few hours the account is closed. Just closed an HHonor card using this method this afternoon.