RETENTIONS IS THE WORST!!!

My contract expired in July and MTN expects me to call them to cancel. I called the call center and they put me through to retentions. Worst all center experience of my life. I was put on hold for over an hour so I gave up. I called a second time and still put on hold for an hour before I hung up. I decided to send a mail but still no response after 2 weeks. And they say I can't cancel over email. What must happen then? You are not returning phone calls and im not getting through via the call center. All I know is if the debit order goes off this month or anytime after, I will be reversing it. I don't have time for nonsense!