No refund for faulty product

I bought a roll of 0.2mm flex (R158) 8 Nov 2021 from ACDC Express in Somerset. When I separated the wires to strip it, the copper strands of one side became exposed. I returned it hoping to have it replaced. Other rolls did not exhibit the same flaw. I was told by the salesman, after he consulted the manager, that they can't refund because it was cellephaned wrapped and that I needed a proper wire-stripping instrument which was clearly false. I was forced to buy another roll from the same shelf which showed no signs of the same flaw