Witholding discounts due on Biztalk contract - still no resolution after 8 months

From June 2019 Telkom has been withholding discounts due to me associated with by Biztalk account. Since then I have been in contact with the accounts and sales departments on a monthly basis with countless reference and dispute log numbers and promise of "back-office" resolutions that have come to nothing. All I have discovered is that: 1) there is zero communication between sales and accounts with both of them claiming the other department is responsible for fixing my account billing code; 2) supervisors are never available to assist and it appears there is no manager with oversight over both sales and accounts that can identify the actual business area responsible to sort out the problem; 3) no-one ever calls back or responds to messages; 4) rererrals to this mysterious "back-office" have never provided a fix after 8 months of complaints; 5) all accounts dept can do is credit my discount due in arrears each month only after I raise a dispute. The cause of the problem is never traced and fixed; 6) there is no continuity at all regarding my 8 month old problem, every month is a new complaint, a new dispute reference, a new denial of responsibility between sales and accounts depts; 7) I am denied any opportunity to communicate with a manager that may be in a position and at a level of seniority to actually resolve the problem that was created by Telkom. What do I have to do Telkom???????