Dont take responsibility for their mistake

I bought a power cable for my external hard drive from Cc Amanzimtoti., but was not sure if it was the correct cable. So a guy named Sir John told me it would work because the specification on the box met the numbers and voltage of the hard drive. (The voltage for the hard drive is 12V) So when I plugged the cable in the power box said it is 19V. So the Saturday morning I took it back and told them the voltage is too high, then John told me it will do nothing to the hard drive as it will only take as much V as it needs. I told them I wasn't sure about the product and that I am scared it will burn my hard drive. He told me again it will not. I asked him what is going to happen if it burns my hard drive and he said I could take it back and he will send it to CC p/town. I went home and as soon as I plugged it into my hard drive the smoke came out of it. I took the power cables back and they refunded me for that. I got another power cable from my brother and now my hard drive is not working. I went back to CC and told them it is broken, they told me I should take it to someone who specialize in it, and that he is not fami**** with these things. don't want to take responsibility