MTN SA Worst billing system

I keep getting statements from MTN, indicating I am in arrears with my account. I am emailing forward and backwards with call centre agents, who clearly do not understand business. This morning I receive an email that: "Kindly be advised that your outstanding balance is R*** ,please be advised that your invoices finalizes on the 27th, payment is expected 21 days from invoice date hence your account is in arrears at the moment, your payment was due on the 17th. The outstanding Invoice is 27 January 2021 for R***x which was due on the 17th. My payment was made on 5 February 2021!!!!!!!!!! MTN SA must be the worst service provider from a billing perspective. They decided to automatically change my payment method from debit order to cash!!!!! On who's instructions??????? I will be porting those numbers to Vodacom.