Query not dealt with properly - BWH - KP

Hi I bought a Goldair 2 Gas 2 Electric Hob GGEH-200 - and got it installed ( the ecletrical part only - still pemding gas). Less than 2 months found the line the stove doesn't work. I call Buliders WH- KP and explained, and the complaints department politely asked if had an installation certificate. I said no, then the gentleman said he would get back to me. True his word a mother gentleman by Given from BWH - KP calls and says sorry mam, you warranty/guarantee is null and void cause you dont have a certificate. I'm like oh ah snap makes sense, so where does it state that for future proposed perhaps I can refer to all these ts and cs and read up on it to make more sense of it. He says mam.sorry that's common sense, this is south africa and that's the law. I'm like...ok sor give me more details as I was not educated upon purchase or any other purchase documents. He says you find it anywhere it's common sense. I almost fainted. I politely asked for him to atleast reference something for me. He said he would, but ofcause didn't. I wrote to hello peter to get someone to please call me to 1. Explain properly with facts i want to exchange this stove for fully electrical 2. I want to buy another one and would like to get proper information before being told about common sense. 3. Train your staff (excluding complaints person as he did what he was meant to do)