I used to have that problem on my Streetmate R. Cleaning them religiously didn't help. Brake quiet helps a little bit, but the trick for me was actually chamfering the edge of the pads. Turns out moped pads are just made really cheaply. After hitting each end with a file, applying brake quiet to the back of the pads, and a good wash of the rotor with Dawn dish soap, everything stopped squealing.
Below is a picture of an automotive pad, but what I did looks just like what the red lines are pointing at.