Upgraded with a faulty phone

I went to Telkom The Grove mall and upgraded my cell phone . The very same day the phone gave me problems - apps not opening. I went and stood in the queue again the next day for another phone. Telkom The Grove mall could not assist me with a replacement but the lady helping me advised that a case must be done which can take more than 2 weeks to resolve. Why could you not replace the faulty phone?