MTN removed a debit order without my consent, won't accept responsibility

Added a new number to my running MTN contract around Oct 2018. MTN, in their infinite wisdon, removed my monthly debit order WITHOUT my consent and kept it a secret from me. Imagine my surprise when I get a call from them in March of 2019 demanding that I pay them R2700 or else. Told them I won't pay as I never gave an instruction for the debit order to be removed. It's been one bullying act after another, my lines getting suspended without warning every other day. Every time you call you have to explain the same story at least 15 times to 10 different people, and then they hit you with that old chestnut: 'we'll escalate and get back to you'. Horrible company with cold people at every level whose number one pet peeve is putting themselves in the customer's shoes.