The customer sued me for apperantly switcthing material that he bought on his project. can you help?

I am a local business owner that did work for a customer 4 years ago. Ha had all of his materials shipped to our shop. Now he is claiming that we used different materials ( which we did not) and still have the leftover materials that we used on his job. The fist court case I lost, I was ill prepared. Also he never paid us for the job he is suing us for. I have found information online that talks about that specific material going bad ( which is why he is suing us) Also the manufacturer warranty does not cover usage on recreational use ( we did his boat) I am certain he knows all of this and is suing us because it was his lost.