What to do about a new phishing scam

My problem is with a bombardment of phishing emails that contain attachments.  This seems to be a new scam.  What they do is send emails using my email address (I am not sending these) to non-existent email addresses.  They contain attachments which I believe to be malicious.  Xfinity has no choice but to return these bogus emails to my inbox as undeliverable)  I cannot block or filter them out because, in essence, they are coming from Xfinity!  The emails that come look like this:mailer-daemon@comcast.net.......Permanent Error

In the past 4-5 days I have gotten about 50 of these.  I have been forwarding them to abuse@comcast.net.  Today when I tried to forward 3 more (after the 14 that I forwarded earlier in the day) I received this error message:

Message could not be sent to the following recipients:["abuse@comcast.net"<abuse@comcast.net>] (550-550 5.1.0  Message sending error for >username@comcast.net>

Is comcast getting tired of hearing from me?  I thought They cared about the security of your customer’s accounts.  All of these emails that I have forwarded have headers and lots of coding.  Why can’t they do something about this??

[EDIT: Name]