Hassle with returning poor quality purchase.

On 23/05/2020 I bought a Lawn Star combi mower / trimmer from builders warehouse Somerset West. I used it for the first time on 24/05/2020 on my lawn, and I had not even got half way through when the whole mechanism that holds the blades cracked, and actual blades snapped off. I took it to return, and Builders Warehouse Somerset West told me I had hit a rock and they would send it away to the manufacturer to assess and confirm this. I said no, obviously they will not accept responsibility for making a poor quality product and agree with you, so I took the broken machine and told them I would lodge a complaint. It is a poor quality device and I want a refund.

Firstly, I know I did not hit a rock, as I would heard or at least felt it. Secondly, if I did hit a stone, which gardens do have lying around, it was so small I didn't notice, yet the machine was broken from it, meaning it is a poor quality machine and I dont want it.