The CRAs, for their own internal business reasons, do not want accurate information deleted from their files, and thus have a policy, incorportated into their credit reporting agreements, that instructs all furnishers not to delete their reporting based on payment of the debt.
Many organizations thus have general policies, passed down to their employees, that deletion should not be granted based on payment of the debt.
Continuing to call first-line employees is likely to get the same result.
I sugges calling someone up the managment chain who has authority to grant an exception to their normal policy of no-deletion.
