Automatic Transmission problems of the 2006 Mini Cooper Convertible

I bought my Mini cooper two months ago. It is a 2006 model. I was driving home on the night of Thursday January 7th when I heard a loud clunk. I live on a caliche road so naturally, I thought I had kicked up a rock or clunk of dirt and it hit the body of my car. The next morning I headed out to go to class and less than 5 miles (I live outside of town 30 miles, so yes I do a lot of driving, but my 2004 Hyundai sonata handled it for over 2 years and when I first acquired it had 145,000 miles and when I finished 198,000 and was still running fine) down the road I braked to turn onto a different road and after completing the turn I pressed the gas pedal, the engine roared the tachometer sprung up, but the car didn't move. The mechanic I took it to confirmed that my transmission is shot, no doubt about, however he cannot tell me exactly what is wrong with it without taking out my transmission and looking at the inside as that is where the source of the failure originates. It is an internal defect that consumers have no control over.