Mediacom blames router for internet problems. Moline, Illinois

I was watching one of mediacom's tech repair service.  The tech installed new wires on the outside of the house and then in the house.  The tech stated that the problem was the router, the tech said he directly connected the computer to the modem, and yes there was internet service.  

The computer was connected to directly connected to the cable modem before the new wires were in and there was no service.   I'm not sure how the wires got back in to the router.  

I do computer support for customers and contact the cable company often, and 90% of the time they blame the problem on the inside of the customers, which is not right.  Out of the 90% of the time it turns out to be a problem on the outside wiring.