MTN South Africa poor service

I had a contract with MTN for over 6 years. Last year October my contract was ending and I decided not to renew. I called MTN several times and I sent emails to their retention department in order for them to cancel the contract. I eventually received a reply from them a month later followed by the phone call which was confirming that my contract will be cancelled and that MTN will not be deducting from my account the following month. Monday the 4th I didn't receive calls but I thought my clients were still on holiday, to my surprise later that day I realize that my sim was actually blocked. I called their call center and I was told that I owed MTN a thousand plus and that is the reason for my account being blocked. I sent an email to MTN customer services and cc'd all the email addresses I had used previously to communicate with them, to this day they have not gotten back to me or even acknowledged my emails. I am not without a phone and I use that line for business. All I want is for them to sort this mess up and never will I ever deal or recommend them to anyone I know.