MR Price Mobile selling faulty phones

I bought my sister a cellphone from the store in Queenstown, the following day the screen was just blank… Initially we thought okay heres a red flag because the phone didn’t fall or get any damage it just decided to be blank on its own.. The blank screen eventually stops being blank, a day later the screen was showing ink marks… i went back to the store as i wanted them to refund me or give me another phone because clearly they sold me a damaged phone. It was less than 7days when i took the phone back and they are busy speculating that i dropped my phone or sat on it while im telling them that never happened. To cut the long story short they booked that phone for repairs, i want my money so that i can but my sister a new phone that wont have any problems. Im so disappointed in the service we got