They screwed up my oil change in almost every way!

Hi,
My car is a '01 VW Passat GLX V6. I took my car to a very well know place for an oil change. I know that VW are somewhat specialized and called first to see if they could handle the job they said yes. Instead of the oil change I asked for they drained my transmission, over filled the engin with oil, and one of thier services is to check and grease the chassis if need and they totally didn't do that either because the CV boots on both side are broken and it is obvious. I drove on the car for 4 days before the problem was caught what should I do? I know that this could cause far reaching problems for me that the garage may not find right now. What are they liable for? Please Help me. Thanks.