Mechanic fails to repair an oil leak, who is responsible?

I own a 2001 Oldsmobile Aurora (3.5 V6) that had a pretty significant oil leak. I took the car into the shop and was told that it also had a coolant leak, which really was not a surprise. The mechanic initially estimated the repair at $400. I agreed and went about my business. About a week later, I had not received word from the mechanic so i decided to give him a call. The job was going to be larger than estimated and it was left at that. I waited a total of three and a half weeks for the entire repair and was charged $950 total. Granted it was a surprise how long and how much it cost but I wanted to ensure the job was done right. Needless to say, whenever the car is parked, the oil stains reappear. I took the car back and they said it was a coolant overflow hose clamp and had replaced it. I am 99% sure it is an oil leak due to the location, texture, appearance, and odor. My question is, do I have a right to a free repair or even a discounted repair to actually fix the problem? I only ask this because I have heard that these engines are notorious for having multiple leaks. The shop has an "a+" BBB rating and all the mechanics seem to have sufficient ASE certifications. Any help or advice would be much appreciated.