Disappointing Service From Defy

I've had to log a request three times for the same problem. My fridge makes aloud noise as if something is rubbing against the fan. The moment I open the door, the noise stops. It happens randomly and it seems that the fridge is not defrosting which is causing an ice build up which in turn results in the noise. The technician that came out the first time said that I should clean the fridge and see if it makes a difference. I did so but the noise returned after a day. The second technician (Manfred from Appliance Repair Centre) said that three sensors need to be replaced. He said that they will order the sensors and come fit them once they receive stock. A few weeks later a different technician arrived to install the sensors. He only replaced one of the sensors saying that the other two are still fine. Lo and behold, two weeks later, the problem has returned. I've always been a Defy customer as previously, your appliances were of good quality. Recently however, your level of quality has dropped way below expectations and this is very disappointing. If you cannot fix the issue, I suggest you refund my purchase price and come fetch your fridge. I'd much rather buy a different brand that knows how to provide a decent service to their customers!