Aggrieved mtn client

I have ordered an iPhone 13 with mtn but then I think the was a miscommunication and they delivered an iPhone 12...I called and they told me to return it back to any nearest mtn shop which I did...I was told to call back and submit the IRMS number, which for the past 3 days I have tried to do that, they keep putting me on hold, transferring my calls then hang up on me...this happened for the past 3 day...such bad service I have never encounter in my life, and I wanted to re-apply for the correct one but since this happened I am having second thoughts