Dont add more yeast, again just keep agitating the existing yeast and raise the temp. You'll definitely see more attenuation, even if the beer is already at 7.5. 1.020 is just way too high for the yeast to be done working.
You might want to post your actual recipe in the thread. I'm not sure if many people are willing to d/load an attachment to view your creation.
Anyways, I'd reduce the amount of C-80 to 2% and add 2% of caramunich (really rich red tone).Also I would reduce the amount of chocolate to like 1-2%...