Specifically, for cable companies:

Cable companies are monopolies granted the privelege of operating in your area by a local governing body.

Call the cable company, and tell the person you talk to that you have had technicians come out, but they have not understood the problem, and you need someone with instruments that give more information and better understanding of the situation. Tell them a person across the street has the same problem, so it is a problem with their network, not with your wiring. Tell them that if they cannot send someone out with the expertise to solve the problem, you could gather signatures from the two blocks or more worth of paying customers, and submit those signatures to the city council (or similar for your area) noting that requested service has not been carried out.

I talk tech, so I have never had to go that far. I have had to explain the situation to an installation supervisor, and have even had one come out to determine the problem, but you might have to treat them like the proverbial donkey and hit them over the head with a 2x4 to get their attention.