Bad custumer service

I took my phone for repairs on 06/04/2015 as it had a signal loss and battery fault. It is still under warranty. I went back to enquire if if was fixed on 13/04/2015 only to find that my phone was not fixed at all. It was brought back by the repair centre on 08/04/2015 with a note that they have mixed up the documents and tranfered my phone with a wrong package. I asked them why they did not rectify it and have it returned to the repair centre, I was told they did not know it was back but they signed for the delivery note. Now I have to wait again for it to be taken back and I was told it will take another 7-14 days. I have thus been without the phone for more than a week which nothing has been done to it so far.