neXT M1 Cellphone (MTN)

I bought a cellphone next M1 (includes the smart watch) from Ackermans on Sunday 27 August 2017 - Game City. Firstly the box was not sealed, it was the last one left, so they took the last phone from the glass cabinet and off I went home. The next day I found (after unpacking it all) that the screen has a lithium mark on the brand new phone screen, off I went back to Ackermans. They contacted the supplier of this phone and the supplier had automatically stated that "IT IS THE CUSTOMERS" fault, (bearing in mind this person hadn't even asked to see the phone) therefore I would not get a new one nor would I get refunded (what the hell) now I'm sitting with this damaged phone (heartbroken) as it is brand new. I don't know what else to do, who to contact etc Can anyone please help ?? Thanks