If an employee doesn't take care of this for you here, Comcast Security Assurance might be able to help. Give them a call at 1-888-565-4329 (from http://constantguard.comcast.net/help/report-abuse/). Note that this is NOT one of the general customer service numbers.
The first-line reps there are sometimes not very helpful. If so, be persistent, and keep at them until you get a satisfactory answer.
Without their help, the only thing you can do is turn off spam filtering completely so that everything they deliver is placed in the Inbox.