MTN BAD SERVICES

I am very disappointed by the service I've received from MTN just after I finished paying my contract with them. I took a contract of two sim cards in August 2016 which was a 2 years contract meaning my last payment was due in August 2018 which I have paid in two payments (on the 10th and 12th of August 2018). I was then advised not to phone or do anything as it will automatically close after the payment..... But now I'm receiving calls notifying me about R800 balance that is outstanding and I have been handed over to the lawyers. I then called MTN customer service to find out how did this happen I was told that they've been communicating with me to inform me with the situation in a form of email but unfortunately the email address that they've been sending to is incorrect. To my surprise since my last payment in August 2018 till to day there was no communication at all. All I want is for my name to be cleared because I paid up everything that I had an agreement with MTN... I very devastated how can MTN do this?... This is the worst experience that I've ever had with big companies such as MTN... I need this fix... Please hello Peter help resolve this issue.