Find another one similar to yours, and get a look at the mechanism with the hood up. You may be able to snake a hook made with a coat hanger in from underneath, and pull where the cable connects.
I had to do this with an old Peugeot. Wound up taking a headlight out, because there was no finding another Peugeot to see how the mechanism worked. Persistence is your friend. And.....Don't put the hood back down, until you have the mechanism sorted.