Forced device

So yesterday i went for an upgrade by mtn de anker in Rustenburg. The sales lady told me that they only have iPhones SEs en 12 minis in stock. After i made peace with the 12 mini and started a process. Another random customer walks in and they find a mystical IPhone 12 64 gig in the same store room for him

What do i do

I have an iPhone but after having the mini for a few hours that was forced on to me i have realised that its way too small for me. And i want to know why was it necessary to lie about the stock in the store. MTN help