Business Banking withholding interest due and non-responsive

On 20th May, we flagged to the Business Manager at FNB Business Banking that no interest had been paid to our business account since March. The account receives large deposits, so the income foregone was considerable. The Business Manager promised to revert by the end of the week. Ever since then, we've been regularly following up, with repeated empty promises made. Still no interest, financial or human, 3 weeks later. Business Manager is uncontactable on her number provided.