Had the same thing happen to me with a 95 C280..

You are on the correct path.. Take it to multiple body shops until one can figure out how to open it..

I went to about 3 body shops before my hood was opened.. He pulled up on the rear of the hood on the drivers side to access & remove the hinge screws and some of the front fender screws. This gave him enough clearance to see the release hinge/cable in the front. Then he used a long trigger pliers (pliers at one end and a squeeze handle at the other) to grab the cable. Yanked on the cable several times and voila, it opened.

We then replaced the release cable and installed a bicycle secondary cable on the hood release for emergency hood access. the bike cable is accessable from just above the front tow hook.

Good luck...