if the vehicle was sold before the GM bankruptcy GM stated it is not responsible because , the old GM is dead.
the vehicle being 8 yrs old is past any warranty. you are resonsible.
GM does have ABS failures on most all of the vehicles they have produced. the controlling systems are of a defective design and in the wrong locations with brake lines that corrode .
No way is GM going to pay for this repair. though my guess is that repair shop did damage something when they worked on it . perhaps a electrical connector or a ground .
what happened exactly when the brakes failed ? examples PEDAL TO FLOOR / PEDAL PULSATING / HARD PEDAL WILL NOT DEPRESS / PEDAL GOES TO FLOOR AND WILL NOT COME BACK UP TO NORMAL ?