My Golf TDI mk4 had its timing belt changed 3.

My golf tdi mk4 had its timing belt changed 3 thousand miles ago and as I was driving I lost all power. I had taken it back to the mechanic who previously had changed the timing belt. He had told me the engine mounting had come off and gone into the timing belt tensioner. I believe he is trying to con me as I have been told that unless the engine mount is corroded it should not have come off? I have researched and found to change the timing belt you have to take this mounting off. I am just wondering where I stand as changing engines will cost too much as I am a student. Is there any way to prove that this mechanic is at fault? Thanks luke