Cellphone complain

Hi there I am very disappointed with truworths galleria mall and I bought a new cell phone from them and December 27 last year so when I got home I only noticed that the phone has a problem it opening on the side I send the phone back to the and they told me it a physical damage guys I am paying my account evrymonth and I'm paying for something that I don't have and I don't use how fair is that and how can I pay R4000 for something that I know it their fault I hope you guys can help me with this matter thanks