Sony Xperia 4 with repairs for 5.5 months

Sony Xperia 4 with repairs for 5.5 months. Phone , still in a contract ,handed in 23 October . Todate the phone has not been repaired or replaced.. Keep getting the reply ...Cannot get parts .. Then No replacement stock . I have R 209 pm , that is more than R 1200 for the last 6 months with a single minutes usage . This is bad service . Bad Bad and totally unacceptable. Bertus in fairness he is telling me that all is being done , but after 6 months something needs to happen. I feel patience is not going to do it. The phone , I understand is currently with vodacare where it has been for sometime. I am due for an upgrade but I need this issue satisfactorily resolved .Your assistance is needed and will be appreciated. Many Thanks