Bad service

I’m so disappointed in the service I got at cash crusaders klipfontein in Witbank bought an iPhone 6s last week Friday and I was told it was a brand new phone but all of a sudden the battery is doesn’t last even 4hours even on battery saving mode...all I want is for them to give me a brand new phone as promised and I’m not welling to waste my petrol and go back there they need to make sure that I get my that phone before course what they doing it’s false advertising and giving customers false advice