Poor service, poor quality appliance

Bought a Obac gas oven the 29th of Novemebr, it was delivered and all looked good. The oven does not work up to standard, loosing heat and not maintaining heat whilst bking. A call was logged 2 days after we recieved the oven, an Obac technician came out to assess the problem and eknowledged that the oven is faulty and that he will submit a report. Now Bawas claims that the problem is no longer their problem (I paid them for the oven) it is Obac's and that the technician cliams that the oven is working 100% but they will replace the elements in the oven. Why if the oven is working, will they replace elements? Why if I have nout used the faulty product can they not replace it with a working one? DO NOT BUY APPLIANCES FROM THEM!!!!!