Early warning signs should never be ignored, especially when it comes to accessing the engine. You may have to damage your plastic grill to get the cable to release because MB was good about covering the release mechanism to keep out would be thieves.
Go to the left of the center rib just below the release tongue, take a long screwdriver, use a flashlight, and poke a hole in the plastic cover to get to the release mechanism. You will need to work at it so be patient and you will get it.
I had to do several throughout the years, good luck!