Mtn bad service

I app**** for iphone15 in October 2023 with mtn and they said I don't qualify because my credit score is low so they advised me to take a Sim contract for 2 months so I can improve my credit score. I called them they said I must pay the Sim for 18 months so that I can qualify for iPhone 15, I went to the branch in Ferndale mall they said I must wait for 3 months in order for me to qualify. Now I want to cancel this contract and when I call them they are not helping me.