Poor telkom accounting

After upgrade of contract by telkom they decide to only deduct the newly upgraded contracts amount and not the others, after paying it myself with left to the details they provide my account still shows I am in arrears. When I contacted telkom they said it is a limit placed on my account, for what reason would anyone want a limit lower than the total amount for all the contracts due. After resolving the debit order it still shows an arrears amount on my invoice. I want this resolved