Tablet phone

i bought a cellphone on the 28 june 2015 from game store soshanguve crossing mall.when i arrive at home i found that my phone does'nt work properly on the speaker,on the 3rd of july 2015 i went back to the store within 7 days from the day that i bought my phone to log a complain in order for them to exchange it with proof of purchase and the whole package.i explained everything to department manager then he refused to assist me with exchange or refund,he told me that he can only take my phone for assessment in order to be fixed then i gave them my phone as they explain that it will be fixed and it will take 21 days to be repaired.they called me after 21 working days to come and collect my phone,when i arrived at home trying to receive calls,i found that my phone still having the same problem,it have\nt been repaired according to the way i expected