MTN is listing innocent customers on credit bereua

MTN is a terrible company I had a contract in 2018 i paid my account in full. When cancelling my contract in 2021 I was not owing anything and the agent confirmed it cancelled. This year I found out that they listed me on credit breau for 143.00 I went to MTN shop and I paid they told me they will cleare name In a week because because I'm not arrears. Since July I've been calling them and sending emails to legal department requesting for a paid up letter no one has assistede. When calling them they answer the call and talked in background without helping after that they cut call. I've been sending emails still no one get back to me.MTN legal department they don't care about their customers they only ruining my name for something that I do not owe their service is very poor.