Faulty handset

On the 1/072015 I did an upgrade via the call centre and on the 6/07/2015 I received the handset. Three days thereafter the phone started freezing. On several occasions I spoke to the person that sold me the phone, Mr. Gregory Muthen telling him about the phone. I was told to take it to the nearest Mtn store for them to send it to the repair centre. I told Mr. Muthen that I will not because our Mtn store only work with repairs and I don't want my new phone to be repaired, I want a brand new handset, as it was not my fault, it came faulty to me and Mr. Muthen also agreed that I will receive a new handset. Mr. Muthen then made arrangements and the courier services came to pick the handset up. After a week the same handset was returned to me. I MEAN REALLY? From that time I am still struggling and hoping someone will help but nothing. I even spoke to the Supervisor Slindile Mdubo but NOTHING BUT NOTHING GOT SORTED OUT!!! The time I received the handset back it was finishing my data, my air time etc. I want Mtn to reimburse me and they even deducted the first installment without resolved the issue. Reference no's: ***, ***, ***, ***1. Pls help!!!!