Poor customer service

I’m on Mtn and I took an Mtn contract phone and Mtn delivered the wrong phone to me an iPhone 7 and afta 2days they delivered the iPhone 11 and I took the phone back to an Mtn store in carnival mall and I was assisted by a guy named Sam and he gave me an IRMS number and he told me to call Mtn and cancel the phone and I did just that bt Mtn continued to take money in my account and it took money in my account for 6month ..I kept on going to the store carnival the same Sam assisted me and he sent an email to Semeshnee Munusamy sales assistance and Mtn promised to refund my money bt they didn’t till this day ..and it’s a lot of money I need back my money