After so many years of support this is what I get from MTN

I have been a MTN prepaid user for more than 10 years and decided to take a contract phone with them. For the first few months debit orders went through my account as agreed, then September 2019 my debit order returned thinking they were gonna deduct twice the coming month. To my knowledge they were deducting their due debit order only to find out that they have handed me over to their collection via an Sms I received in February 2020, I have not received any communication from them advising me that they were not receiving payments for four months, on top of that I never advised them not to deduct and money was available in my account because to my knowledge they were deducting. I contacted the MTN helpline and they were unable to answer my questions and advised me I must pay R1500 outstanding balance, one of the consultant offered to escalate the case(***) to their Legal department and I got no help. I spoke to the collections company that I was handed over to, I spoke to a consultant called Lerato and she advised me to pay the outstanding amount then she will request for reactivation from MTN. I paid the outstanding amount due to MTN then after a few days She called me back and advised me the reactivation amount is R2000, how am I liable to pay this if it's not my fault that MTN was no longer deducting their monthly R350 installment? How am I liable for this R2000 whereas MTN never communicated that they were not receiving their payments? After so many years of support this is what I get from MTN.