Fed up

I am so fed up with Defy Service. It has been seven weeks since I logged a complaint. My gas oven would not get to correct temperatue and is still within the two year warreny. A technician came out but could not fix it. It was collected two weeks ago. I havae tried phoning. Only once managed to get through a week ago. Was told I would have it back within two days. Huh. Still cannot get through, the phone just rings. Here on facebook I have complained....was told someone would contact me by yesterday. Not a word. They have my stove, for which I paid a lot of money as I wanted one with a grill. Is it theft if they haven't returned my goods in good working order? I am at the end of my tether!!!