What could be wrong with my brakes?

A few days ago I took my car into the shop because my driverside rear brake area was making loud dragging noise whether I was using the brakes or not. At time is would sound as if the muffler had fell and was dragging. I was told that the cylinders had a leak which caused the hardware to rust and break. I had them fix it and put new front rotors. They had kept calling with problems they 'just found' and when they called to say my car was ready the guy says they just noticed that my brake booster was going bad. $300 and 4 days later I'm driving down the highway (not using brake at the time) and I hear clunk clunk. As I'm gettin off the highway I hear the same exact noise I had taken my car in for! Except this time its worse! There's more grinding and some squealing when braking. What could the problem be? Could it be a botched job?