Damaged phone

Took out on a contract with mtn on the 28th May 2015 for a Sony Experia Z3, when I got home I realised that the phone's wi-fi is pushing up the ping of a wi-fi network, it took 2hours to download a app. I then took the phone back on 4th June 2015 to return the phone and identified the problem with the consultants. They then said that they will have to send in the phone for repairs. It has been 6weeks later and I still have not recieved my phone back. Every time i walk into the shop they say\sorry they are on strike"I then got Gavin's shop number to phone him as he said \"" Sir it is my off day tomorrow and I will come in specially for you to phone our courier company to find out what is going on\"" he didn't pitch for me.. I spoke to one of the female consultants and she said \""sir your phone is on the way it will take 48hours for the phone to arrive this was on the 9th of July 2015. When I phoned now on the 11th of July 2015. They told me the phone is still not there"