Out of The Box failure and unacceptable service

Did an upgrade 2 weeks ago - Sony M4 Aqua - had to do a SIM swap for smaller sim. It activated 4 hrs later so couldnt test in store. Found we can not hear clearly during a call - very soft /far away. Took the phone back following Thur - they told us they had to check it in - and take up to 7 days for technicians to look into it. Following Tues told us that the technicians couldn't find any fault with the microphone/speakers and we can come test in store. They had lost my son's sim card so we tested with a prepaid sim in store. It worked perfectly - loud and clear. They then did another sim swop for my son's postpaid and that activated 2 hours later at home. We had exactly the same issue. Menlyn insist they have to send it back in again. I called call centre on Friday to cancel the upgrade and the contract. Ayanda from retentions told me she would escalate because store should replace the device and she would call me back Fri/Sat. She didn't call and when I called on Sat I was told retentions don't work on a Sat. Went to Menlyn and they refused to give us a new device as they don't want to lose money. Have been unable to reach Ayanda today. Will cancel this and my other 3 lines ASAP