Bad customer service

I was trying to buy a cell phone yesterday at Edgar's in maponya mall and then the assistant was so rude that she did not want to assist me with the phone I wanted then I went to the manager for assistance, then she told me the phone I wanted is not there anymore but she did not want to sell me the one that's on the display, yet she couldn't answer me when I asked her why is it still on the display. I help on how to deal with this.