hell my FA had the same problem, what i did was i took the brake pads out, which were completely worn out, formed a cast in Styrofoam cut small grooves, in what was remaining of the brake pads, and cast a new brake with jbweld. After it set, take the newer pad out, and file it down, until its smooth. Worked like a charm... stopped the scooter, and the squealing.
Ps, did you make sure the brake pads were aligned properly, tht would make them squeak too