Bought Sony Xperia M 4 Aqua that was faulty

I bought a Sony Xperia M4 Aqua at Vodacom 4 U @ Carnival Mall Brakpan on 26 June 2015 and went to rica a new sim card as it takes the nano sim . After a day phone still did not pick up any signal and I though maybe it will take 2 days for registration so I gave it another day . Then after another day I decided to take the sim out and test it in another phone and it worked perfectly !!!! So on 28 June 2015 I took the phone to Vodacom 4 U @ Carnival Mall Brakpan and they tried to Rica another sim card and also tried to put the sim in different ways and after a while decided to book it in as they apparently did not have stock to replace the phone that was brought back before the 7 day policy they have !!!! Then the cashier said they will have stock on Tuesday and that I can come and pick up my new phone !!!!! I phoned them every day since and everyday they have another story and they say they will phone back but never phones back !!!!! I just want to know what is going on , I either want a new phone or my money back , this is ******** !!!