I hate saying this, but they did not check the pads. They may have visually checked the outboard pads looking thru the wheels, but they did not check the inboard pads by pulling the wheels and calipers.
That high pitched noise was the wear indicator and the grinding you hear now is the brake pad backing plate eating into the brake rotor as there is no more brake pad friction material, so you have metal to metal grinding of the backing plate on the rotor.
It will need new pads and rotors. You dont want to drive it at this point. The reason is because the brake caliper can only extend out so far before it pops out and you lose brake fluid and the brake pedal goes to the floor. Safety wise, it should be towed to a repair shop
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