Cannot cancel data sim cards - worst service ever at MTN Retentions

I have been calling and emailing retentions to cancel 2 data sim cards for months. Each call gets transferred and cut off. emails gets responded to but nothing the 2 numbers are still active and I keep paying for them. It seems I will have to cancel the debit order in order for anyone to pay attention. Worst customer service ever after I've been loyal for 20+ years. I am moving over to another service provider.