Overcharged on a wrong package that was delivered

I have an iPhone 11 with MTN so a consultant call to offer me a deal for 199+R9 for sim and router, upon delivery they delivered a sim only when I called they said I can cancel it and later reapply.Now I’m supposed to pay R561 for my IPhone but on the app there is an outstanding balance of R1149; claiming it’s for a cancellation fee, monthly fee and pro-rata; mind you I cancelled the very same day it was delivered, why must I pay cancellation whereas they delivered a wrong product, monthly fee and prorate for what because I didn’t even use that SIM card. MTN gave me a ref no BO*** It has now been 3 weeks with no change on my account, on Friday I was told to call Mondo and was given a ref no KL8E5BQ. Today Mondo tells me to call MTN billing department for adjustments now MTN billing tells me that Mondo was supposed to cancel on CPI so that the bill remains on R561 for my IPhone. How is this my fault that the consultants cancelled this the way she did because I’m not even aware of the CPI method, I just want to see adjustments on my account coz if they debit R1149 I’m going to dispute it. The contract is for MTN so why must I do the runaround with Mondo and MTN.