who is responsable for outside cable

For a number of years i have had cables running over the roof As i live above and behind a shop
now these cables have been there 13 years with no problem
until last week the owner of the shop downstairs is now complaining that the cables are
sagging into the valley which runs between 2 buildings causing moss to accumalate
What i want to know who is responsible for making sure these cables are secure me
or the installer Virgin Media
I want to know before i call them so they dont try to get out of doing the job
which was supposed to have been done properly when my cable was 1st installed

Cozmikangel