You need to get the grille off to get at the bonnet release catches, there are two. Trouble is the two screws retaining the grille are covered by the closed bonnet.
Prising with a screwdriver may be an option but with two catches would require 2 people working simultaneously and there is always the danger letting the screwdriver slip and holing the radiator as a wellmeaning friend did to a 99 I once had.
Under the circumstances, getting a more substantial grip of the cable with Mole grip and getting a good pull on it may prove more effective.