the supplied cable has a built in isolator - thats needed if there is no isolator in the internal box - maybe i am misunderstanding or maybe you are not being clear - what have you got internally - what is the 'other' cable - post some photos - they are better than lots of words that could be misunderstood
Ok, so from the box on the outside wall, the cable with red arrows comes inside through the white box shown (through the TV connection though so I guess that’s not what I need?) And ends with the shown connection which would connect to the hub if that was appropriate?
I’ve also circled in yellow the end of the cable connected to the ntl box - I guess this is a defunct connection?
ok - no idea whats happening outside so lets ignore that for now - 2 choices inside
1 - if the end of the cable you show goes back to the internal wall box and is screwed into the bottom connector then connect it to the hub - power it up and ring for the hub to be activated - try 0800 953 9500 afaik thats an automatic activation number
if that works the power light should eventually go white and you should have internet
if it does not work then try
2 - unscrew the cable from underneath the internal wall box and add the new cable and then connect the hub and try the activation again
if neither of those work then it would look as though there is a fault outside although it looks ok
go from there - if you have not opened the external box and the cover is missing you still need a tech to sort that