contract termination

I took out a 24 month mobile phone contract with mtn, 3 weeks before the end of my contract i contacted mtn to let them now that i would like to terminate my contract at the end of the 24 months, i was asked to let them now 3 weeks in advance which i did, i received an email to let me now my request had been sent along with a reference number, 2 months later i received a call from mtn threatening me to pay despite me telling them my contract had ended i was then subjected to more threats shortly followed by the lady slamming the phone on me, i have tried to contact mtn with no luck so iv resorted to the one place that can help thank you