Tech service fee but tech support didn't mention AND was faulty gateway

Thanks for the fast reply, but my initial post didn't set the stage for my situation.  It was not a self-install as there was no Comcast cable to my house.  The original tech needed to throw down a cable from the Comcast exterior street hub to my house and install a box on the house siding.  When I got service running everything seemed OK, but as I got more time with the service I suspected that there was a problem.  That's when I started running very frequent network diagnostics (pings every second to the 3 destinations) that showed it was the gateway.  (If the gateway doesn't respond to a ping across ethernet...)  When I had this info I contacted Support, and story continues as in my OP.  Part of the problem convincing Support there was a hardware issue was that their remote diagnostics showed that service was OK, when the more granular diagnostic I was running showed the frequent, very short (usually :01-:03 seconds) connection drops.  

As a side note, that cable laid on my front yard for almost 10 weeks before getting buried, despite multiple promises from Chat Support that it would be taken care of; "in the next week" (4 times), "in 24-28 hours" and "tomorrow".  None of those happened.  It was finally buried last week.  

Thank you for this additional context; it is greatly appreciated. Any exterior work needed to get a working signal to the home can be necessary, depending on the home location, but still be part of a self-activation.  We can certianly look over the account and any notations to help provide any solutions. 

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