RAC Mechanic has wrecked my engine/car

My car was immobile on my drive on Saturday the 19th of December 2015, it would not start. I called for assistance and was visited by an RAC mechanic. On arriving he suspected the timing chain was at fault. Despite this he tried repeatedly to start the car but stopped after a loud bang. As advised I took the car to a garage and after initial investigation they reported the piston in no 2 cylinder had hit and snapped a valve. After dismantling the engine the damage was such that they recommended a new engine (£3,400) as the best course of action. As you might imagine I feel badly let down, I am not an engine expert but know the advice with regard to suspected faulty timing chains/belts is don't try to start the engine AS YOU ARE GOING TO DO SERIOUS DAMAGE. I now think I should have intervened but just accepted the mechanic knew what he was doing. Faced with a repair to value ratio of 75% or so, I decided not to repair the car and sold it on as it was for £1,000. So the mechanic’s mistake has cost me my car which at the time must have been worth £5K. Had I just taken the car to the garage I don’t think the outcome would have been the same.
Since then the RAC via the customer care representative who dealt with my case have refused to accept responsibility for their mechanic’s mistake. To make matters even worse (if that’s possible) the representative during a recent telephone conversation admitted to me that he had not even read my communications on the incident. What kind of complaints process is it where the complainant’s side of the story is ignored? when I asked if I could speak to his Manager or someone higher up in the process the representative told me that was not possible.
So on the face of it if the RAC get the service wrong there’s little the customer can do about it.