Store Manager would not exchange faulty Cellphone!

Good Day,<br> <br> I recently purchased a cheapy cellphone (Nokia) at MTN Promenade Mitchell's Plain on 20th Feb 2016, as my expensive cellphone was ****** the Friday prior. I took the new cellphone phone home and started using it. However, I found that it was faulty and took it back to the store. The store manager (Masnoena) checked it and said she couldnt find any fault with it. I explained to her that when I make a call the call just cuts, she insisted that there's nothing wrong. My mom is currently using the phone, as I was struggling with it. Now whenever I try to call her to that same phone I have to dial her number trice before the call goes through. There's clearly something wrong. I am NOT satisfied with this phone. What do I do???? Please help??? Upset customer. N