extremely poor and false selling by MTN representative

MTN claim I owe them 1600R,I tried calling them several times with no valid answer from them, cancelled my contact with then in 2020 ,few months started receiving messages from MTN,at first it 100Or went to my nearest store and was told it was system migration,to my surprised it never got fixed to date,when I call I get a different story telling me that it my invoice bill,I asked for the recording of my contract no answer from them

Please help me,my credit record is a mess because of MTN