MTN Attorney lack of service

My MTN was handed over to Norton Lambrianos Attorneys, the last payment I made was last year November, I had no deductions afterwards from my bank account and I assumed I have completed my payment on my contract. When I called them today to get a credit settlement letter to confirm my payment is complete they told me I still have over R5000 to pay. And when I called, they informed me that there was not enough funds in my account which was impossible since I wait only after the 30th of every month to use my funds after my outstanding debt is paid. When I asked why I didn't receive any contact from them, they informed me that they sent me an sms as a reminder. I'm not using the number they sent the sms on since the phone is broken. I have asked why no email was sent to me informing me about the outstanding balance or a call made to my alternative contacts , since they could call me everyday to get a hold of me on them when I stopped making payment when I lost my job the first time, no answer was given. I am very very upset because my account would've been 1 - 2 payments away from done now and now I have to pay more than. I spoke to the supervisor who gave me a call back regarding my account, and she advised that sms is the only notification that will be sent, no email, phone calls or even post mail which I find very weird and unproffessional. To be honest I feel like I should not be paying the previous months for the lack of communication they have given regarding my payments that had to be made and don't think that I should pay the full amount that is over R5000.