After service BAD

My wife bought a Defy oven gem gourmet on the 16th of August 2014 from the store in Umgeni Park Durban. In January 2015 the stove started tripping our main's, I report it to the store and a technician was send out after several calls to come and replace the element on 26/01/2015. On the 29th of June 2015 it starting tripping the mains again , technician came out and told us that this will happen if you turn down the heat from 190 to 150 degrees?????. No repair was done. ON 3RD OF AUGUST 2015 I PHONED AGAIN BECAUSE IT TRIPED AGAIN WITHOUT CHANGING THE SETTINGS. I SPOKE TO COLEEN NAIDOO AND UP UNTILL TODAY NO ONE MADE CONTACT WITH US YET.