Defaulted me for a contract I had finished paying for.

From June 2018 I took a 24 months contract with mtn which was due to end in June 2020.I settled the contract the even called me offering me an upgrade which i declined and asked for the contract to be closed.Fast forward in July 2021 i went to open a credit at another store only to be told that mtn had defaulted me for owing them R144.50.I than wrote an email to mtn to query this matter on the 31 July 2021 still to date 7 September 2012 I have not received a feedback but on the automated response they say you will receive feedback in 24 hours for me it has been more than a month waiting for a response.I curse the day agreed to take that contract,I didn't know it will destroy my name like this.