Handed me over to debt collectors without even contacting me and I didn't even know that my payments were bouncing

I have a 'device only' contract through MTN and for some reason my debit orders have been bouncing (I suspect the debit order was set up through my credit card which was recently cancelled as it was lost). I got a phone call from a Debt Collector yesterday to say that I need to pay MTN the balance of the entire contract. (about a year to go still). MTN did not contact me to notify me that my account was in arrears or that they were going to hand me over.

Firstly, I am not in financial distress so this could have easily been rectified if the had just tried to contact me using the contact details I provided them when I took out the contract.

Secondly, my credit record will be affected by this lack of customer service which is completely unacceptable.

MTN: Please contact me to resolve this matter. Your call centre is pathetic and cannot put me through to anyone who can actually discuss the matter at hand.