Just had new brakes put on 3 months ago an noticed black dust, and a squelling noise for weeks now when I aply brakes it sounds like metal grinding. What could be the problem?

They may have installed semi-metallic disc brake pads, which are aggressive and often cause noise and rotor wear issues. I would go with Wagner Thermoquiet Ceramic Pads, guaranteed for life, where you won't see dust or experience squealing. Ceramic pads last long, stop faster, run cooler, and won't damage your rotors. Bottom line: They likely installed the wrong pads for your car. The should have been organic or, preferably, ceramic pads.