******* : company refused to refund or give me voucher

I am so annoyed on how ShopRite handled this. I bought a kettle on 30 June , have the slip and the kettle is still in the box with everything. I used it and it was not switching off after the water is boiling. I then bought myself another kettle at another shop. Today I returned it and when they were testing it apparently , there was a loose cap that I needed to fit hence it was not switching off. The fact of the matter I have already bought myself another kettle so why are the forcing me to keep this once and I don't want it because I have one already. They are asking me why am I returning it because it's working and they don't want to refund me. The lady that I spoke to at the shop spoke to the branch manager who then told me they can't take it back. I don't need money even if they give me voucher for the mount because I have a kettle already now.