Poor Quality Product

I purchased a Defy stainless steel gas hob. Within days of boiling rice on this appliance, it began pitting. A complaint was lodged accordingly. Three technicians, on three different occasions, arrived to investigate the issue. All gave us an undertaking to submit a report and have the appliance changed. This happened after the third event. Two days after the new appliance was installed, the pitting began. Another complaint was lodged. "Technicians" from Defy's sub-contractractors arrived with a toolbox to attend to the problem. How does one repair pitting with a box of spanners? My wife explained the problem and again the technicians left with a promise to submit a report and have the problem resolved. On checking with Defy's call centre, the complaint is logged as completed. Attempts to contact Davison and Rodgers from Defy's service centre has proven futile. Defy's need to provide an amicable resolution to this problem and not take the word of *********** people for granted. I, as the customer, am highly discontented with the level of service received. Please address urgently.