Debt management costs are charged if you have not paid your invoice(s) on time.
Late payment interest is a charge for the time you have delayed payment of your invoice(s). The amount payable for non-performance is the amount provided for in the contract (or by law), which usually depends on the extent of the default and the length of delay in performance, and is fixed as a percentage.
Interest is a payment to the lender for the opportunity to use the money. Interest can only be claimed if it was agreed to in the contract.