Mtn has failed me as a valued customer

Good evening ,last month I had called Mtn , telling them I am not renewing my contract with them and had requested them to close my account. After that my number was changed to pay as you go. Furthermore this month I paid my last debit. I then called yet again requesting for a settlement letter but still no luck as no one was giving me the service I was expecting as a valued customer. I was on the phone for an hour , making things worse I was in a Mtn Store while calling customer service as staff at the store also failed to help . I'm very frustrated as I want to buy a house and need to provide a settlement letter , showing I am no longer on contract with Mtn. I have paid this account for the past 2 years without any fail now this is how they thank me.