Poor workmanship

The pants came, in the mail. I tried them on, they fit. There was nothing visually wrong with them. I put them in the wash. When I put them on, I noticed a seperation about 4" long, in the outer seam, above the left knee. Because they fit nice, I disposed of the paper work, before I washed them. I sent an e-mail, to the company. They claim I damaged them.Bob