AUP Violation

I received an email from Cox about AUP violation. Accessing the Cox account at the Violations page there is a download of a copyrighted movie (Viacon Inc)

Cox email is assertive to do not contact them because it's a message from a 3rd company and Cox is just forwarding.

How to address this question with Cox?

I'm totally sure that I didn't download this movie. I already changed my WIFI password and also did a modem factory reset.

Thank you