Towing Issues: vehicle damage from tow, tow truck driver, professional towers

Question
I recently got my car stuck in a deep snow bank, and used my road side assistance membership to get towed out.
The driver was dispatched in a small pick-up truck, not a tow truck, and he attached a cable to the underside of my car to pull it out.
After about 5 minutes of trying to pull my car out, he flagged down a passerby in a larger pick up truck, and proceeded to attach my car to this other vehicle.
He then got in my car, put it in reverse, cranked the wheel all the way to the left (I was in the ditch on the right side) and I watched in horror as my car was dragged accross the ditch, rear wheels in the air, and finally pulled out of the ditch.
I questioned the tow truck driver about his methods a number of times, but he insisted that he knew what he was doing.
I took my car immediately to a GM dealer nearby and had them check for damage (I noticed a loud whining noise right away)
They informed me that my transmission had been damaged, and needs costly repairs.
I contacted the towing company, and they agreed to take full responsibility for repairs, since numerous mistakes had been made.
However, when I brought my vehicle to their repair centre, they refused to repair it, saying that I couldn't prove that the damage was caused from the tow.
I also noticed that the car is not as fuel efficient as it was before this happened.
Any advice on how to proceed?
Thanks

Answer
Have you tried contacting your road side provider yet? Most professional towers would agree a pickup truck and a strap is NOT an acceptable recovery method. As for the transmission damage it's possible it was damaged before the operator even hooked to the vehicle. There's many different scenarios and would discuss in further detail if desired. I do understand from what you witnessed that the operator could have damaged the transmission as well. From what was witnessed it's harder for the tow company to prove they did no wrong doing as the operator did operate the your vehicle. As for the fuel efficiency that could be expected from a poorly operating transmission. Hopefully you and the tow company can come to some sort of agreement to settle your situation, good luck