SMDS MIdas - Selling Reject or possibly pirated SPARK PLUGS

I purchased set of 4 NGK plugs for my 2012 Hyundai accent on Monday 25 June 2018 from Midas SMDS shop 2 1 Kosi Place, Springfield Park, Durban for R380. My mechanic installed the plugs that afternoon, I drove into CBD and returned that evening, the engine started to flutter, fuel consumption was high and it did not sound smooth like the plugs I had replaced which were purchase from Autozone a year earlier. I took the vehicle back to my mechanic next morning, he test drove vehicle and confirmed the plugs were not working correctly, so he removed the plugs and put the old plugs back and the vehicle returned to normal smooth idle and no flutter. I took the plugs back to SMDS Midas and explained to the owner the problem and he checked plugs and said plugs were running to hot and gaps not correct so he had them adjusted. I told him I was not happy with the plugs and wanted a refund, he says nothing wrong with plugs and asked me to wait as NGK rep was in area. A Mr. S Maharaj arrived claimed to be manager of NGK plant appeared with a small tester, he checked the plugs and said there is damage on plugs due to overheating, he put it into his 1.5 volt tester which shows there is a spark from plugs. The store owner called the NGK rep to back office and several minutes later both men return to tell me there was nothing wrong with plugs because it sparked on the tester. I explained that the NGK rep just told us there is damage to plugs and I asked for a refund. NGK rep said he cannot lodge a claim and SMDS Midas owner says he cannot refund me. It was clear these two men were working hand in hand. So I took the plugs back had my mechanic who reinstalled them and did a road test , those plugs were just as bad as before and the fuel consumption was of the charts. I had my mechanic reinstall my old plugs and they were absolutely fine and fuel consumption returned to normal. I believe these plugs sold at SMDS Springfield Park are either rejects or possibly pirated plugs. These plugs will damage my engine and cost me dearly in absurd fuel consumption. I want my money back, and if I don’t get my money back, I intend reporting this to Wendy Knowler on East coast radio, on other social media platforms and taking matter up with Consumer Ombudsman as well as contacting NKG to have these plugs tested for quality.