Unhappy service from vodacom

I didn’t know vodacom selling second hand phones when u do a upgrade ! I been having endless problems since day 2 I took delivery of it from the store , been at the store to change but must book it in for repairs ! How can I person get a new phone an after the second day book in for repairs an it will take 7/14 working days ... been at the store 3 times !!! It’s a 2+ drive an the response i got giving I’m highly upset an when I call the call Centre I get a question how must they help me with the problem no assistance was even offered !