Unhappy client

Good morning,I would like to complain about MTN,they sent my name to Nudebt and credit beuraeu saying I owe them R1700 and I owe them nothing,I had two contracts with them and I was paying R838 every month on the 15th,and one of my contracts was ending on the 12th of February 2021 ***) and I called them before that date to cancel it and they did not do that,I even sent them an e-mail to cancel my contract,still they did not do that,they only called me to upgrade and I said no,I asked them to transfer me to their cancelation Department and still they didn't do that,they were sending me from pillar to post because I did Not want to upgrade.I'm only left with one contract ***) which I'm still paying R600 a month until next year January 2022.Kindly assist me with me this problem