Sales person defence and attitude of a manager

I went to mtn for an iPhone 7 plus contract and only to get the iPhone 7 and sales person **** to me says its the same phone and everything is the same yet when I arrive at home to my girlfriend and she told that she **** to me its not a same capacity of space a this phone was for her and I tried contact the lady and she said its out of stock and yet she didn't offer to order one, nevertheless I found out that even this iPhone is not insured as I've asked her to insured it and she said she did.my girlfriend lay the complaint to Clinton the manager and he was so rude in the call and finally said we must bring the phone back after asking if it's sealed and now when we went there the phone is sealed and the cardboard is not as the sales person opened it so he refused because of cardboard and also he said I signed for the phone so he can't change it and also it has already passed the 7 days yet I contacted the lady the second day I present the phone to my girlfriend.i asked for regional manager email and explained to her, she called the meeting and she told us she can'tdo anything she issticking to what Clinton says and they were defending the sales last though they see she was wrong. And the sales lady agreed to pay the phone and they said she can't do that we must take this phone back and they were laughinh durinh the meeting as I have record of the meeting

What do you do with this.please help