Item bought Physically Damaged cannot be returned

I bought some goods from Computer Mania in Somerset West Mall on 25 January 2015, including a USB cable (CABLE USB MICRO MALE 1.5M). I have a copy of the receipt.<br> <br> The first time I used it (removed from the packaging and plugged it in immediately), I noticed after some time that my device was not charging.<br> <br> On 30 January 2015 I attempted to return it, but the salesman said the cable had \physical damage"";and I get to keep the USB cable they sold to me in a \""physically damaged\"" state.<br> <br> This is really silly on their part"