AWS Blacklisting?

I have a customer who's suddenly been getting 403's today on AWS hosted sites.  My google-fu seems to be failing me because I can't seem to find any information on who manages that on their side or how to fix the issue. I've sent an email to amzn-noc-contact@amazon.com based on ARIN contacts, but it doesn't seem to be a responsive address. Has anyone had to navigate this particular maze before? Thank you, Justin H.