Bad costumer service

Bought a cap on the 1 October for R500.00 in Vanderbiltpark store washed it once and the stitches started coming off. When to complain about the stitches and was told I was negligent, used a hard scrubbing brush. Only the stitches are coming off and the rest is ok. How is it possible for a hard brush to only affect the stitches and not the whole cap.