You could dial + 359 32 933 900 (if you are already in BG – dial 032 933 900) and give your complaint regarding corruption or similar behavior of any police officer that you have come across.
The phone is open for complaints 24/7 and a message machine can record your call within 3 minutes of your call.
It is advisable the complaints to be non-anonymous fore better results and fastest measures to be taken. But even if anonymous all complaints will be taken into considerations and never ignored.