Brake light not working
 

2011 Jetta Sportwagen TDI, have a warning message and light about left rear brakelight out. Sure enough, blown bulb. Bought the correct replacement bulb, installed it, but still the brake light is not working, and dash warning message and light still on. Checked all fuses, all ok. Bulb receptacle seems clean and not corroded.
I am a bit baffled, any ideas out there?