Dun (verb)

1. Make a persistent, urgent demand for payment or action.
2. To press or urge persistently for payment or action.

Origin:

Middle english: from old english dunn "dull brown", of germanic origin; related to dutch donker "dark", german dunkel "dark", also to dank.

Examples:

1. The debt collectors have been dunning him for months for payment of the outstanding debt.
2. The company was dunned by the supplier for the payment of the overdue bill.
3. He was constantly dunned by phone and mail for the payment of the credit card debt.
4. The landlord had to dun the tenant for the overdue rent.
5. The creditor decided to dun the debtor for the unpaid loan.