Vodacom sold me a damaged contact phone

I got a new contract iPhone on Friday the 7th of December 2018 at Vodacom ****arney mall. I started u sing the phone on sarturday afternoon by Sunday the phone was heating up and had ink on the bottom right conrner of the screen.

The following Monday I took the phone back to the shop, explained to them what was happening I told the sales lady I want a new phone , of which they refused and told me that I dropped the phone , of which I didn’t I told her I want a new phone or I cancel the contract because It was still within the 7 days period . She told me they are taking the phone for repairs first which will take between 7 to 14 days , But the phone had issues not even after 24 hours I opened the box why can’t I get a new phone or cancel.i left the phone at the store.

No communication wa made I was the one who had to follow up , she went silent for a week until I decided to sms her only to tell me that I have to call the call center to cancel the contract of which I did only to be told I have to pay over R5000 , ooh by the way the found out that it was a factory faulty with the phone not my faulty.

I returned the phone back at the shop within 7 days can’t I cancel the contract in peace please!!!!!