Frustrated with MTN Billing

The MTN billing department is deplorable. I was surprised to get an SMS from NuDebt advising that I owe MTN and should pay to avoid being blacklisted. Immediately I called NuDebt asking how does MTN hand over my account to an external party without even contacting me to advise that my account is overdue. What's even more appalling is that MTN collects their money via Debit Order and none of my debit orders have ever failed. I have sent a copy of my bank statement to NuDebt and they have referred the issue back to MTN.

Recently I checked my credit score and it has been negatively affected by MTN saying I owe them money. Its been a month already and MTN is sending me from pillar to post with stupid emails regarding this. I cant call the legal department neither can anyone from their department call me. They say I must pay, PAY WHAT? I am no donor to a corporate.

Please MTN get your act together and resolve my account and reverse the negative judgement on my name you sent to the Credit Bureau.