We have a Kitchen-Aid convection microwave oven, that hasn't worked properly since we bought it 2 weeks ago, The service rep has been out twice to try and fix it. He states that there is an obvious problem with the unit but his service manager won't allow him to replace the unit. What recourse do we have

Check for class action lawsuits on that appliance. There are many, like the one on GE refrigerators a few years ago. What is the problem?