Unable to cancel MTN contract

Extremely poor service. I have a number of reference numbers from Customer service, retentions and complaints, but everyone passes the buck without resolving the issue. I had a data only contract which expired Aug 2020. In spite of my instructions not to renew the contract, MTN continues to present the Debit order. I have been corresponding via email, messenger and Facebook, but still only promises and no action. MTN branches are unable & unwilling to assist.