3rd Party Spam Service and Exchange Receive Connector

We grew tired of all of the spam and decided to sign up for a 3rd party spam filtering service. After getting it up and running and relaying our email to Comcast, we noticed that spam was still getting through. Apparently what is happening is the spammers are sending spam through the back door to the Comcast mail server and ignoring our MX record.

So, what needs to happen is we must implement a setting on the Comcast Exchange side that only allows email in when it is coming from our anti-spam company's servers. This requires configuring our Exchange Receive Connector to listen for one of two specific IP addresses. 

I called Comcast Business tech support, waited 35 minutes on hold, and they had no idea what I was talking about. (shocking)

How can I talk to someone at Comcast who is an expert in this area and knows how to get this set up?

Here is an explanation of what we need:

https://technet.microsoft.com/en-us/library/aa996395%28v=exchg.150%29.aspx