I recently bought a new bike which I paid £2700 it's carbon and has Di2 groupset. I am not going to name manufacturer and the shop that supplied it yet. The third time I used the bike which had about 40 miles on it by this time and was 10 days old the rear mech sheared off. I was in mid cassette at the time and the bike had not been dropped at any time. The frame got chipped and the rear mech cage was twisted. It did not damage the wheel. I returned the bike to the LBS and the usual questions were asked. They suspect that the chain was the problem. They returned the bike to the distributer and they are going to replace the parts under warranty. They will not tell me which parts they are replacing. My question is what should be replaced? The frame has light damage. The rear mech cage and pulleys were twisted and the hanger was obviously snapped. Remember the bike was only 10 days old. Your opinion would be greatly appreciated.