Cox Communications Set up an email to pay a bill for unknown account San Diego California

You have described a classic PHISHING attempt. You got an email from someone having nothing to do with Cox, and likely not even in the US. 

Phishing is the fraudulent attempt to obtain sensitive information such as usernames, passwords and credit card details by disguising oneself as a trustworthy entity in an electronic communication. Typically carried out by email spoofing or instant messaging, it often directs users to enter personal information at a fake website which matches the look and feel of the legitimate site.

The tell-tale signs is that it was an Email, if Cox(or any company) is trying to collect a bill they would send you a letter or bill in the mail.

Second the e-mail had only your First and Middle Name, likely where ever the scammers got your name from didn't have your last name(and don't you think your EX would know your last name?).

Third, if you checked out the e-mail you would find that
a)It has a lot of grammatical errors
b)Any link in the email goes to a "phishing" site that will look like the Cox site but is not.

They will send out 10's of thousands of e-mails and if they get even 1-2 to fall for it, it is a success for them.  Sometimes the e-mail will have the legitimate contact information for the company, hopeing that people will just click instead of calling. However, many times any contact information will also lead you to the scammers. Had you actually actually gone to the site and logged in, the scammers would have taken your information and used it for stealing your identity.

Cox has no record of an account, and all the SDPD are going to do is take a report. As there is nothing more for them to track down. The best thing to do in this case when you get these types of e-mails is to just delete them and move on.