The homeowner is NOT liable except in the unlikely event he stood there and told the fence company "dig here," and that was where the cable was--in that case, he was at fault and, being at fault, can be held liable. Assuming that did not occur, the fence company is responsible: it was their employee(s) who negligently (carelessly) failed to take precautions to identify buried utilities (including cable line) and who cut the line; that is, it was the fence company's fault, and being at fault, they are liable, or financially responsible, for the damage.