King Cadillac Buick GMC

I sent my pontiac g6 to find out why my brakes were locking up. Was given a bill of 580 bucks where the boosters were done. Take the car home the brakes lock up again. Took the car back and was told that there was nothing that they could as they could not determine what the problem was. So my husband took the car home. I called the dealership to address my concern of the problem not being fixed and the staff tried to smooth things over and "promised" to try and find and resolve the issue. Set up the appt to bring the car a 3rd time well guess what not only the person I spoke to was not there for the appt but nothing was done to the car other than test driving it. The staff admitted they experienced the brakes locking up on them but make out they still didn't know what the problem was. Then spoke to my husband and actually told him that another 135bucks was needed to do another "look" at the vehicle. Ok why wasn't This thorough look done the first time?? This time I felt like it was a process of elimination expedition that was gonna cost us even more money. Then I get a guess of maybe it's the calipers.. well who's to say that this was the issue oh and did I mention that this was going to cost roughly 800 bucks ..so we just cut out losses and took my car home with the issue not being resolved..what a waste of 580 bucks..