Self-install billed for broken cable passed demarc point

Did a self-install.  Got no connection on my modem.  Was required to have a tech come out.  Tech decided a new run from the demarc point outside of the house to the comcast equipment in my backyard was needed.

I got charged $40 bucks after specifically asking before the tech come out that if it wasn't my fault I wouldn't be charged for anything.  You guys said I wouldn't be.

This clearly wasn't my fault.  The tech touched nothing inside my house.  ALL repairs were made past the demarc point on the side of the house and it was all Comcast equipment and cabling that was faulty.  Why am I charged with this visit?  I want it refunded. This is absolutly rediculous.