No Service from Defy

We have literally been waiting 4 months for a working thermostat for our oven. The technician came out 2 weeks after we called the service centre. He discovered that the thermostat was not working properly and the door's hinges needed replacing. We then waited 3 months for the thermostat as there was no stock. The technician finally returned and installed the thermostat. We then realised that the thermostat was also not working correctly and logged a follow up. The technician came a few days later and confirmed that the oven was 30 degrees hotter than it should be. He assured us that they still had thermostats so he just had to get one and bring it to our home to install it. It's been 3 weeks now and we're still waiting. We messaged the technician directly last week and he said he would come and install it the next business day. Still nothing. We recently had to replace our washing machine and we did not look at a Defy. The appliances are good but the service is near non-existent.