The three motor phase wires are switching the full battery voltage across the motor while the Hall sensors are powered by only 5 volts. During the time while your brake disk was sawing thru the cable, it probably short circuited the battery voltage across one or more of the three hall sensors inside the motor casing, blowing them out.
Someone has to take off the side cover of the motor and replace the sensors. All motors are different, so maybe someone already did it on your motor and posted a youtube video.