VERY BAD SERVICE WITH DEFY

I have a stove that was bought from defy and installed in my house in August last year, the stove started giving me problems in December. I logged a call with them and they only came 3 weeks later to fix it, then a serious problem started after the first fixing. i would keep on having problems and logging a call for a technician with them. the technician came for the 5th time and he confirmed that the stove is dead and it cant get fixed, i then went to defy personally and they referred me to their manager who then said he will send a senior technician to come and look at it, he then came after two weeks and it was fixed for 3 weeks and the same problem persisted again, 2 weeks ago i then reported it again and they said they are sending a technician he only came after 10 days, the very same day he came when i switched it on it was not working. i don't understand why defy cant just change my stove and give me a new one as they can see that this one keeps giving me the same problem and they are failing to fix it. it looks like this stove had a factory fault from their store and right now it is not working, am not sure if i should call them again because they cant seem to help me with anything.