For 3 months since I bought my phone it's broken

For 3 months now since I bought my phone I have been complaining about Vodacom Somerset Mall near Entrance 3 that sold me a broken phone. This Is the 3rd time in 3rd time that I am posting this complaint on Hello Peter and every time I post Vodacom sends me an sms that my complaint has been logged and that someone is going to contact me but then nothing. The one-time a guy phones me back and tells me the store must not make their problem his and he will phone me on that Saturday at 1pm then I must be at the store then he will sort them out and I went and sat there the whole time waiting for him to call back and I am now awaiting a return call for 4 weeks. Must I cancel my debit order? This is by far the most disgusting service I have ever experienced!!