Fails to remove adverse listing after paying off loan

I had a loan account with African Bank which ended up arrears due to unforeseen medical and legal expenses, the bank then listed me at the bureaus as an adverse. Although monthly payments were being made the bank continuously updated the bureaus as a missed payment. After the estate was wound up i received partial funds of which bulk of the outstanding loan amount was paid to African Bank at the end of March. The bank updated the payment at the bureaus however they failed to remove the adverse listing. I have mailed them and called them but get told its 21 working days to update. Its updated almost immediately for them but takes a long time to remove, this is just ridiculous. This is also now impacting me as i can not qualify for a home loan even though i provided the paid up letter to the various institutions. The adverse listing is bringing the credit score down. Although i advise the bank to resolve urgently they still fail to act in a timeous manner.