How do I let Yahoo know I'm receiving undeliverable messages for email I never sent?

My quess is someone is spoofing my email because I am recieving undeliverable messages for email I never sent. Yahoo doesn't seem to provide any real way to contact them. They provide an ever looping help page. My guess is that they don't really want to know anything, but at least this shows I've tried to let them know.
How do I let Yahoo know I'm receiving undeliverable messages for email I never sent?
Yahoo's customer service is execrable. But you need to check your firewall provisions -- someone may be using your machine remotely to send spam.