I want to cancel my contract

I upgraded my contract last week Wednesday the 6th of December , All was good and I bought a screen protector for my new note 8. The guy who installed my screen protector didn't install it properly cz over the weekend I realised that the screen protector was coming out and on Monday I went to cresta mall to get it changed n some lady told me that I need to go to the store where I bought the screen protector, And I asked that why because I had a receipt and they could check on the system and just give me a new one besides mtn os mtn no matter where I go. So today 13 December i got a chance to go to Clearwater mall and the screen protector has come out and it was in my bag cz I called in the morning telling them it came out and they said I needed to bring it. So it happened that it cracked while in my bag and I was only gonna go to Clearwater mall where I bought the screen protector after work. So I got there and they tell me they won't give me the screen protector they need to consult and based on that a decision will be made whether I will get a new one or not. That thing costs 300 and now I need to buy another one after a week? I don't think so. All i want to tell you is that I want to return your phone since you don't value me as a customer and the fact that I have been with mtn for almost a decade. I will also not be paying any cancellation fees just take your phone and leave me the **** alone. I will gladly come bring it.