Failure to debit- unfair arrears charged.

I have had a cellphone contract with Telkom Mobile which has been debiting funds from my account without any issues until the past few months where they stopped debiting without informing me. I have phoned in countless number of times to query why my account is not debited on the agreed upon date and all I get from the consultants is that they will escalate my query and phone me for feedback. I have not received any feedback until today where I got an sms informing me that my account will be suspended due to failure to pay. How is it my fault that even after I had followed up to ensure they debit that they end up not doing so? Instead my account keeps accumulating arrears which are expected to be paid by myself even though I have never had any issues with paying! Telkom has not tried to inform me that they are having trouble debiting my account, I have been the one following up to ensure they debit, yet they don't. I am not prepared to pay for these arrears because I have tried to get Telkom to debit from my account on the agreed upon date and they have to failed to do so without any explanation. I need them to reverse these arrears and keep debiting on the date that we agreed on.