回複：回複：Mr.Bigbelly,pls give opinions

I am terribly sorry if I am repeating an obvious point. You should send your letter in the post office and pay for the return signature service. In so doing, you will then have proof that the bodyshop receives your letter.

It is good if you additionally call the bodyshop and essentially repeat the same thing in the letter. You do not have to argue with them -- just say the necessary and then end the call.