Brake Disc problems of the 1998 Saturn SL2

Not long after we purchased the vehicle, the brakes made noise and caused the steering wheel to vibrate upon braking. Brought in the vehicle for service and they said the rotors were warped, they cut them down. Since then the brakes have made noises and the rear wheels lockup upon initial driving daily. Each time the vehicle was brought in for regular oil changes, we complained about the noises, at 10. 209 miles &16,284 miles, but they always said nothing was wrong. Now the brakes are still making noises when you first start the vehicle. Also, now the steering wheel vibrates upon braking, more at higher speeds, causing harder braking at times when quick braking is needed. Upon slow rolling stops, like coming to a light, the car surges, like the brakes are grabbing at certain points then releasing. Sometimes braking in normal city roadways, the brakes don't respond when quick braking is needed to avoid dangerous situations. It's like the brake pedal is tough to press.