Experience trying to close an MTN account

I cancelled an MTN contract over a year ago over the telephone my account was in order and it was confirmed. i have invoices that even prove the account was cleared for months and then suddenly my account is sitting in arrears for an amount of 700+ Rands. I did not have a contract for R700 this amount did not accumulate over months from my original contract amount. I have been in contact with MTN lawyers via mail to clear and close the account. I have sent affidavits, invoices showing the account was in the clear. I being blocked from make purchases due to this account. I keep getting messages to contact CSS however the number is unavailable. Its unacceptable that credit score is held ransom by an amount i do not owe.