From the IHG website (via the virtual assistant that pops up when you click the "Need Help?" link):

Guest Relations:
The phone contact details are:

• Telephone: +1 855 914 1701
• Fax: +1 801 975 1846

Please note that these are only domestic US numbers.
You may also contact Guest Relations via email at: [email protected]

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Just to echo hotelboy's statement, any complaints made about a hotel via the contact information above will be sent to that hotel to be resolved. If you didn't get any concrete response when emailed the hotel, that's not likely to change if you contact Guest Relations at the corporate level. The exception to that would be if the hotel had clearly violated a policy or rule. In that case, the corporate office may offer some form of compensation and bill it back to the hotel.

To be clear, I'm not saying that you shouldn't try. I'm just trying to set appropriate expectations.