Faulty Samsung S4 mini

Hi there<br> <br> I need an urgent assistant, I took a contract phone with cell c late last year. the phone Is constantly giving me a problem the speaker and the mouth piece is faulty i.e. when I speak the person ill be talking to cannot hear me at some times. I have booked in the phone twice already to be repaired but the problem is still not solved.<br> <br> I will really appreciate if someone can urgently solve this matter I am not prepared to book this phone for a third time. I need a new device or kindly cancel the contract.