MTN charged me approximately R19027 for early concellation

I have two (02) contract lines with MTN that I opened with them. In November R1443.00 was debited from my account by MTN , when I asked them as to why I was told that opened a new line. I told MTN that I never opened an additional line. They told me that I had to send an affidavit and my I'D copy and I did. Few days later I received an sms telling me that the case was resolved. So every month they are harassing me with the debit amount of R19336.27 messing up my bank account and my credit record. If I call their 808 number their consultants keep asking me to explain what happened over and over again. They also suspended my services for more than 4 times telling me that my account is owning R19336.27. I don't know what do do anymore.