Horrible service

I'm highly disappointed with MTN's handling of contract cancellation especially as I have been a customer for over 2 decades. I provided the requisite cancellation notice and the billing date fell on the cancellation date. At the time of cancellation, I was not informed that this will be an issue. My contract was subsequently cancelled and immediately converted to prepaid with all balances forfeited. However, I've been invoiced for the period post the cancellation. When I call and speak to the consultants they agree it does make sense but I receive emails saying the invoice is correct. I'm highly frustrated as I'm constantly being told the date of the cancellation falls after the billing date and as a result I am liable for a period I was neither able to utilise the service or provided with data on lieu of the amount I'm expected to pay. I paid for the outstanding amount and now when I want paid up letter they are taking me from one department to another . It has been weeks now calling their customer services and email them with no lucks .